Some models are programmed to adjust to Greenwich Mean Time and British Summer Time automatically. These boiler timers automatically adjust to GMT/BST:

  • DT20 twin channel digital programmer
  • DT20RF digital RF thermostat with twin channel programmer
  • TD200 text display
  • FW100 weather compensation controller
  • FW110 programmable room thermostat

Most models feature a battery back-up which will remember your settings during a power cut. The only exception is our fascia mounted MT10 Mechanical Timer, which would require a simple adjustment following a power cut.

To make viewing and adjustments easier, all fascia mounted digital controls are backlit.

Optimisers respond to changing conditions to ensure the desired room temperature is reached at the right moment, whilst conserving fuel by avoiding bringing your house up to temperature too early. Example: Most households requiring a comfort temperature of 21°c at 7.00am would typically set the central heating programmer for 6.00am.

On particularly cold days, the house may not reach the optimal temperature by 7.00am and on a milder day it may do so too early, which means some energy could have been saved. You can simply set an ‘Optimising’ Room Thermostat to deliver your comfort temperature at your desired time. The optimiser will calculate the perfect time to switch the boiler on, ensuring optimum comfort and the best use of energy each day.

The Greenstar system boiler range can be used with the following controls, provided the boiler is fitted with the Optional Integral Diverter Valve.

i System boilers

  • DT20 Twin Channel Digital programmer (with 240v room thermostat)
  • DT20 RF
  • DT10RF

The hot water temperature control on the i System boilers is achieved using a volt free cylinder thermostat.

CDi System boilers

  • DT20 Twin Channel Digital programmer (with 240v room thermostat)
  • DT20 RF
  • DT10 RF
  • DT10 RF Optimiser
  • Intelligent System Package
  • FR10
  • FR110
  • FW100
  • ISM1

The hot water temperature control on the CDi System boiler is achieved using the cylinder sensor supplied.

For Valley Gas wall-hung gas combination boiler range, the first channel regulates the times of operation for your central heating. The second channel controls the time the pre-heat function takes place. The hot water pre-heat function enables a vastly better response to the hot water tap.

This prevents the boiler firing up out of hours to pre-heat the boiler’s domestic hot water heat exchanger, perfectly balancing hot water availability with economical operation. Hot water is always available, even if pre-heat is timed to be off, however the response may just be a few seconds longer. Please note: Our floor-standing gas and oil combination boiler ranges incorporate a ‘heat-bank’ which stores heat to enable the boiler to produce the high performance hot water you require.

This heat-bank always needs to be hot to satisfy maximum hot water demands. Just as with our wall-hung gas combination boilers, using a twin channel programmer ensures the central heating and heat-bank are always on when required and avoids unnecessary firing of the boiler.

The FW100 controller which is compatible with Greenstar CDi boilers, is a weather compensation controller/timer.

The FX controls enhance the efficiency of the Greenstar CDi combi and system gas boilers and Greenskies solar panel systems. The series consists of:


The FR10 Intelligent Room Thermostat, to provide heating control with standard plug-in programmers.


The FR110 Programmable Room Thermostat, which is designed to integrate solar installations with boiler controls.


The FW100 Weather Compensation Controller, developed to better integrate a Greenskies solar installation with a Greenstar boiler, offering weather compensation control and increased operating efficiency.


The ISM1 Intelligent Solar Module, which is designed to work in conjunction with the FR110 Programmable Room Thermostat and the FW 100 Weather Compensation Controller to enable the system to run the solar panels when the sun is out but will bring the boiler on if the weather deteriorates. This means the comfort of hot water is always guaranteed whilst prioritising solar energy to pre-heat the water.

Martyn Bridges, director of marketing and technical support at Worcester, comments: “Installers now have more options to help maximise the efficiency of any heating system, as these new controls are designed to work together to help solve the dilemma of water heating during the summer months.”

“Maximising the efficiency of renewable technologies is vital and in years to come it will be more common for boilers and renewables to work side-by-side.”

The installation of any of our controls would require removing panels within the boiler. This may expose the installer to high voltages, so installation should only be carried out by an experienced and qualified heating engineer. Failure to comply could lead to injury and/or prosecution.

This is the siphon fill programme. When switching mains power on to the boiler it will fire at a minimum output for up to 20 minutes. The central heating function will be run at a minimum output during this programme.

The boiler is running in its air-purge mode. This can take up to eight minutes to clear after switching the mains power on to the boiler. During this time the pump will switch on/off intermittently and there will be no central heating or domestic hot water delivery until the programme is complete.

This is a feature of certain CDi boilers. The code is activated after 2,324 burner hours and serves as a reminder that the boiler requires a service every 12 months.

You can install a softening device to your cold main. However, you would not be able to use an internal filling link within the boiler. An external link must be installed, situated before the softener. Softened water must never go directly into the central heating system as this could prematurely damage the heat exchanger.

The external filling loop is a silver coloured braided hose which is connected between the central heating return pipework and a cold water mains pipe. It should be located close to the boiler and is often found under the sink if the boiler is in the kitchen. The braided hose will have a valve fitted on either one or both ends. This is one example of what external filling loops look like:

How to use the external filling loop

  1. Make sure both ends are securely attached to the pipes
  2. Open one or both of the valves on the braided hose to allow water to flow into the heating system
  3. Watch the pressure gauge rise slowly until it reaches about 1.5 bar (in the middle of the green section)
  4. Return valves to the original position to stop the flow of water into the boiler

The pressure in the system will usually require topping up once or twice a year. If you find that you need to re-pressurise much more frequently than this, please contact us.

If you are constantly losing pressure in the heating system you could try the following to establish the cause:

  1. Check all visible joints including radiator valves and connections for obvious signs of leakage. Ensure that there are no leaks to any under-floor pipework.
  2. Check that there is no water being discharged from the pressure relief valve (sometimes referred to as an overflow). This pipe usually goes from the boiler through to an outside wall and terminates outside. Check this for signs of dripping. If it is wet, this may mean that the pressure relief valve is faulty.

In either case, if your heating system keeps losing pressure do not hesitate to contact Valley Gas for advice and assistance.

Valley Gas thoroughly recommends cleansing a system as an important part of the installation process. The recommendations within BS7593 should be followed, whilst also paying attention to the appliance’s installation and servicing instructions and any guidelines specified by the flushing agent manufacturer.

It is best practice to cleanse an existing system prior to installation of the new appliance. After installation the system should be cleansed of debris and refilled with inhibitor. Our team is fully conversant with all current standards/regulations relating to this aspect of the installation.

A condensing boiler is able to extract more heat from the fuel it uses than a standard efficiency boiler. It also means that less heat is lost through the flue gases. The term ‘condensing’ boiler refers to the fact that the boilers produce condensation from time to time.

Condensing boilers use heat from exhaust gases that would normally be released into the atmosphere through the flue. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate.

In order to make the most of the latent heat within the condensate, condensing boilers use either a larger heat exchanger or a secondary heat exchanger. All Worcester Bosch condensing boilers are known as ‘Greenstar’ boilers.

The water from combi boilers is heated directly from the mains – so the only time the water is released to the atmosphere is when it comes out of the tap. This means that during heating the calcium bi-carbonate, present in the water, changes to calcium carbonate.

This creates carbon dioxide which close up is seen as millions of bubbles. This is purely an aesthetic affect and does not affect the quality or taste of the water. If you run some hot water into a glass and let it cool it will slowly clear. This phenomenon is more commonly seen in hard water areas and from models with somewhat slower and/or lower flow rates.

Occasionally you may notice a white plume or discharge coming from the flue terminal on condensing boilers. This is due to the flue gases being cooler than in non-condensing boilers.

Whereas non-condensing boilers flue gases are hotter they cool down further away from the terminal and dissipate differently. The flue gases of condensing boilers exhaust at around 55°C and cool more quickly in the atmosphere.

Certain outside temperatures can cause a plume similar in effect to breath on a cold morning.

Water softeners are now commonly used, especially in hard water areas around the UK. If you intend to use a softener unit with a condensing boiler, you must remember that it would be unwise to fill your central heating system with such water.

This change in the ph level will impact the longevity of your central heating system and pipe work. Therefore, it is wise when adding water using the filling loop to your condensing boiler, that this is fitted prior to the softener unit.

When a traditional boiler and cylinder is replaced with a combi boiler, any existing shower should be examined for suitability. This might have been a pump assisted power shower, for example, designed for low-pressure systems.

Combi boilers by contrast produce hot water at mains pressure, which means they are compatible with either a mains pressure balanced or thermostatically controlled shower.

Gas Safe Register is appointed by the Health and Safety Executive (HSE) for Great Britain and HSWI for Isle of Man. Gas Safe Register replaced Valley Gas on 1st April 2009.


The Gas Safe Register is the official gas registration body for Great Britain and Isle of Man. Only a Gas Safe Registered installer is legally allowed to install, maintain and service gas appliances. It is vital that you check your gas installer is Gas Safe Registered. You can ask to see your installer’s Gas Safe Registration card or check on the Gas Safe Register website. If the installer cannot produce an ID card, they are an illegal gas installer. You may like to know that after you have had gas work carried out in your property you can nominate the installation for inspection by the Gas Safe Register.

Valley Gas was replaced as the body responsible for the register of competent gas installers in Great Britain and the Isle of Man on 1st April 2009.

Valley Gas remains an industry body and retains responsibilities for the register of gas installers within Manchester and the Bury.


From 1st April 2005, your local authority must be notified when you have a new or replacement boiler fitted. Your installer should do this for you and issue you with one of the following certificates:

‘Exceptional circumstances’ form

If your installer tells you it is too difficult or expensive to install a high efficiency condensing boiler in your home, they should give you a copy of the ‘exceptional circumstances’ form for you to keep.

Completion certificates

If your boiler is installed by a Gas Safe Register/CORGI-registered or OFTEC-registered installer, you will get a ‘building regulations compliance’ certificate from Gas Safe Register/CORGI or OFTEC after the work has been completed. Gas Safe Register/CORGI or OFTEC will also tell the local authority that you have had a new or replacement boiler fitted.

You should keep these certificates as you may need them when you sell your home.

During periods of very cold weather, we occasionally receive enquiries from customers who are concerned that their boilers are not fully functional. On occasion, the condensate discharge pipe might freeze and prevent the boiler from operating. The following information will assist you in identifying whether you have such an issue with your boiler and what should be done about it.

How can I tell if the boiler’s condense trap/discharge pipe has frozen?

Step 1

It is possible that your boiler’s condense trap/discharge pipe has frozen if all 3 of these statements are correct:

  • your boiler is a Greenstar gas boiler, or a 26 CDi
  • the outside temperature is currently or has recently been below freezing
  • your boiler is displaying either an EA fault code or a flashing blue light (for 26CDi boilers you may see a flashing red light instead)

Step 2

If all 3 statements are true, you should now try to reset your boiler by holding in the ‘reset’ button (this can be found on the boiler control panel) for 10 seconds. After releasing the button, you should wait 2 to 3 minutes to see if the boiler refires.

Step 3

If the boiler does not refire and is emitting a gurgling sound, then it is almost certain that your condense trap is frozen. If you cannot hear a gurgling noise you should still proceed to check your condense pipe.

Step 4

The condensate pipe will be a plastic pipe (black, white or grey), coming from the bottom of your boiler. If this pipe is less than 32mm in diameter and runs outside of the property or through a non-heated area, then it should be fully insulated with waterproof lagging. If it is not fully lagged and the 3 criteria (in step 1 above) apply then it is likely that it is frozen and needs to be thawed.

How can the condensate pipe be thawed?

You should contact your boiler installer in order to thaw the condensate pipe and also to find a permanent solution to the freezing condensate problem.

If you are unable to contact your installer then you could do the following, however, you should exercise extreme caution at all times when attempting to identify and thaw a condensate pipe.

  • You should only attempt to thaw a condense pipe that is at ground level and which is easily accessible to you. Under no circumstances should you attempt to thaw a condense pipe which is at height, without the assistance of a professionally trained engineer.
  • A hot water bottle or heat wrap (like the ones that can be used to ease muscle discomfort) would be a suitable and safe way of thawing the condense pipe. Hold the hot water bottle or warmed heat wrap around the condensate pipe to thaw it.
  • Once thawed, the boiler must be reset. This can be done by holding the reset button in for 10 seconds and then waiting 2 to 3 minutes for the boiler to refire.
  • If you are uncertain of what to do or require particular assistance, then you could invite a neighbour/friend or family member to assist you. The person assisting you can, if required, contact a Valley Gas representative for assistance.
  • Once thawed, you should still contact your installer in order to implement a permanent solution to the condense pipe freezing.

What should I do if I have a different problem, or if following this advice has not worked?
Please contact our Customer Service team on 01685 843325.
More questions and answers about freezing condensate pipes

What does the flashing EA code/blue slow flashing light mean?

There are various reasons that your boiler may display these codes or lights. They do not necessarily mean your boiler is faulty. A frozen condensate trap or discharge pipe could cause these codes – refer to the steps above to check.

What is a condensate trap/discharge pipe?

All Greenstar gas and oil boilers dispose of their condensate by means of a syphonic trap, which discharges a given quantity of condensate fluid at a time to the property’s drainage system/pipe work. The syphonic trap is important because if the condense fluid were allowed to drip continuously to the drain at the rate it was being produced, then there would be an increased risk of any externally run condense discharge pipe freezing.

Why might the condense trap/discharge pipe freeze?

Despite the syphonic trap flushing method, when the outside temperature is below freezing for a prolonged period of time, externally run discharge pipes, or discharge pipes that are run through a cold area of your property (e.g. garage or loft), can freeze, particularly if they are not insulated (lagged), or sized appropriately.

What will happen if my condense trap/discharge pipe has frozen?

The result of this would be the inability of the condensate to drain away, which would lead to the ‘backing up’ of the condense, which in turn will cause the boiler to fail and go to ‘lockout’. If this happens for a gas boiler, then the boiler will likely be showing an EA fault code, or alternatively it will show a flashing blue light and the boiler may be emitting a gurgling sound.

What is ‘condensate’?

Condensate is moisture gathered from the boiler’s flue and allowed to run back through the boiler to a collection point. Condensate is a feature of condensing boilers.

CoP or Coefficient of Performance is the means of stating the ratio of the heat output by the particular technology relative to the amount of energy it uses to operate.

If you’re looking at installing a renewable system into a property, its performance will be dependent on a range of factors.

All the points outlined below are equally important to ensure your heat pump’s performance and efficiency are maximised and running costs are minimised in the long term:

  • Method of construction; concrete and screeds are the ideal partner when combined with underfloor heating and heat pumps
  • Up to standard insulation and U-values
  • Correctly fitted insulation; careless installed insulation will allow heat to escape and renders the insulation job worthless
  • Amount of ground to install trenches – we do not recommend using the slinky method in a trench system!
  • Method of heat delivery and how well the system is installed and integrated
  • System programming and sizing

If the above elements are in place, a heat pump should deliver the following efficiencies:

  • Efficiency/CoP with radiators: 3.2
  • Efficiency/CoP with underfloor heating: 4.6

Expected CoP is taken as an annual average return – obviously in winter it may be lower and higher in the summer.

When installing any cold-mains fed appliance it is important to ensure upfront that your water main is large enough to deliver adequate water to the appliance whilst other cold outlets are in use, for example flushing toilets, washing machine filling or cold taps being run.

Should the water main be insufficient, you may find that cold water is ‘pinched’ from the boiler when more than one outlet is used. You could reduce the chance of this happening by giving the boiler priority over all the other outlets, by piping it up as the first draw off from your mains.

The performance of any mains fed hot water system will depend on the mains water supply offering an adequate dynamic pressure and flow rate, as the flow rate must be sufficient to supply hot and cold water simultaneously.

Whilst there may be sufficient mains pressure the flow rate is dependent on the size, type and condition of the incoming main. It is important not to confuse pressure with flow and the dynamic pressure will be less than the static pressure.

Please see the technical specification for individual appliance mains water requirements.

A water pressure reducing valve may also be required to protect the appliance from excessive incoming mains pressure. Maximum incoming water pressure is normally 10 bar.

A combi boiler provides heating and hot water directly from the boiler. Here is an example of a central heating and hot water system layout using a combi boiler:

A combi (or combination) boiler is an ingenious space-saving idea and an increasingly popular choice in UK homes. In fact, combis now account for well over half of all new domestic boilers installed in Britain every year.

A combi boiler is both a high-efficiency water heater and a central heating boiler, combined (hence the name) within one compact unit. Therefore, no separate hot water cylinder is required, offering space saving within the property.

Further benefits of a combi boiler are significant savings on hot water costs and the fact that hot water is delivered through your taps or shower at mains pressure. So you can enjoy powerful showering* without the need for a pump.

Another benefit is that it can generally save you money on installation time and costs, since no tank in the roof space means less pipe work and a shorter installation time.

* a thermostatically-controlled shower safeguards against sudden changes in water temperature.

Worcester Greenstar condensing boilers supplied by Valley Gas are at least 90% efficient, meaning that they turn 90% of the fuel they use into heat.

The official rating for boiler efficiency is the ‘SEDBUK’ scale. SEDBUK stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’.

Greenstar condensing boilers achieve the highest possible efficiency category – SEDBUK Band ‘A’.

What is a condensing boiler?

The term ‘condensing boiler’ refers to the fact that the boilers produce condense from time to time.

Condensing boilers use heat from exhaust gases that would normally be released into the atmosphere through the flue. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate.

In order to make the most of the latent heat within the condensate, condensing boilers use a larger heat exchanger, or sometimes a secondary heat exchanger.

Due to this process, a condensing boiler is able to extract more heat from the fuel it uses than a standard efficiency boiler. It also means that less heat is lost through the flue gases.

What is SEDBUK?

The SEDBUK rating was developed under the UK Government’s ‘energy efficiency best practice programme’ with the co-operation of boiler manufacturers, including Worcester. It provides a basis for fair comparison of different models of boilers.

The SEDBUK rating is the average annual efficiency achieved in typical domestic situations. It takes into account sensible assumptions about climate, control, pattern of usage and other similar factors.

The rating is calculated from laboratory tests together with other important factors such as boiler type, fuel used, ignition type, UK climate, boiler water content and typical domestic usage patterns. So, for estimating annual fuel running costs SEDBUK is a better guide than laboratory test results alone.

The boiler’s performance is scored, enabling the boiler to be placed in a banding system using a scale from ‘A’ to ‘G’. ‘A’ rated boilers are the most efficient.

Condensing boiler regulations

Building regulations that have come into force since 1st April 2005 state that any replacement or new gas or oil boiler must be a condensing boiler. Rare exceptions can apply. Please ask a Valley Gas & Heating expert for more details.

The Energy Saving Trust is a non-profit company set up by the Government with the aim of addressing the damaging effects of climate change. Working with manufacturers, retailers and consumers, EST helps to promote the production and use of more energy-efficient products.

The Energy Efficient Advice Centres (EEAC)

The Energy Saving Trust has a network of 46 Energy Efficient Advice Centres located across England, Scotland and Wales. These centers can provide householders with free expert impartial advice about saving energy in the home. They will be able to assess each individual’s situation and give advice on what energy-saving measures they can install, and even provide advice on what grants and offers are available for installing the particular energy-saving measure. To contact the EEAC hotline, call 01685 843325.

Energy Saving Recommended Labelling
Areas covered by the scheme:

  • SEDBUK A rated gas boilers
  • SEDBUK A and B rated oil and LPG boilers
  • Central heating controls
  • Washing machines
  • Dishwashers
  • Refrigeration
  • Lighting

Remember – wherever you see the Energy Saving Recommended badge on our website, you know you are looking at an A-rated Worcester gas or oil-fired Greenstar condensing boiler.

For more information about The Energy Savings Trust visit: