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Boilers and Heating

Boilers and Heating Advice/Tips for your home. Ensure a comfortable temperature whilst reducing your energy use, so that you only pay for what you need.

Controlling your heating and hot water

Boiler controls make a big difference to your comfort and energy usage. You can decide when you want your heating, and in some cases hot water, to come on and go off and how warm you want your home to be. They ensure a comfortable temperature whilst reducing your energy use, so that you only pay for what you need when you need it.

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Built-in boiler controls

Your boiler is likely to have two control dials or push buttons on the front, These are a hot water temperature control and a central heating temperature control

The hot water temperature control dial is for setting the temperature of the hot water coming out of your taps and shower,

The central heating temperature control dial is for controlling the temperature of the water that goes from the boiler into your radiators – not the room temperature, It the setting is too high. the boiler will use more energy than it should as well as wasting it

You may also find that the radiators will get very hot and reach the programmed room temperature very quickly. which will turn the boiler off and then back on again when the temperature dips down. This constant on-off action uses more energy, A high setting will also affect the boiler’s ability to condense (capture and re-use the heat that would otherwise escape), which means that energy will be wasted.

It’s also important not to set the dial too low either as the radiators will take longer to heat the rooms to the temperature you want.

Optional controls

Timers and programmers

A boiler timer is a basic device that allows you to set specific times for your central heating system to come on and turn oft, with the same times repeated every day

A boiler programmer allows you to set your heating and sometimes hot water to switch on and off at different times on different days of the week to suit your lifestyle.

Most modern programmers also automatically adjust for British Summertime

A room thermostat monitors the air temperature and enables you to set the level you want, If the temperature drops below this level the thermostat switches your boiler on.


Keeping your system topped up

There are three ways to top up your system, which will depend on the type of boiler you have. Ask your installer if you are not sure which method applies to your boiler. Alternatively, see the ‘Homeowner’ section of the Worcester Bosch website at With all three methods you should turn off the power to the boiler before you start, and stop the process when the pressure gauge reaches 1 bar.

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1. An external filling hose
This needs to be connected manually between the filling link and mains water connection.

External filling hose

2. Worcester internal filling key
This is normally located under the boiler and needs to be inserted into the filling link, enabling you to increase the pressure of your system.

Internal filling key

3. Worcester keyless filling link
This is the quickest and easiest method. It is permanently fitted to certain wall-mounted Worcester combi-boilers and has a lever underneath. To top up the system, simply pull the lever down until the correct pressure is achieved then release.

Worcester keyless filling link

Watch how to top up your system at

Water Supply

Hard and soft water

Rainwater absorbs naturally hard minerals from the ground on its way from the surface to the waterways. Whether somewhere is a ‘hard’ or ‘soft’ water area is determined by the amount of hard minerals such as chalk, lime and calcium it contains. Areas in the north of the UK tend to have softer water whilst areas in the south experience higher levels of hardness.

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Areas of hard water

Hard water leaves limescale deposits on things like pipes, hot water systems, kettles, electric irons and domestic appliances. Over time in areas with very hard water, limescale may build up in the boiler’s heat exchanger, which can reduce efficiency and possibly the flow rate, which in turn can effect your comfort.

If the water hardness count in your area is over 200 parts per million (you can check this with your local water company), this build up can be prevented by fitting a scale prevention device or water softener to the incoming mains,

Cloudy Water

In certain areas of the country. at certain times of the day, heated domestic water might occasionally have a cloudy or milky appearance. This is completely harmless and is caused by the millions of air bubbles (carbon dioxide) that are created when the water is heated. Just like the cloudy water that you might get when you fill a glass from a tap, this will settle and clear.

Combi boilers and water meters

When a hot water tap is turned on and then turned off, a small amount of the water expands, which is allowed to travel back into the water mains under water regulations. Water meters prevent water from flowing back into the mains so if one has been fitted, in some cases there may be a build up of pressure between the turned off hot water tap and the meter. This could cause taps or showers to drip.
If you have a combi boiler and a water meter was already in place when it was installed. your installer may have needed to fit an expansion vessel to the mains water pipework. This absorbs all of the expansion water. If you had a water meter fitted after your boiler was installed, you may benefit from having an expansion vessel added. In both cases, ask your installer for advice.


Radiators use hot water generated by a boiler to warm the air in a room. Generally, the hotter the temperature of the radiator, the hotter the room temperature will be. Radiators are by far the most common form of heating in a home. In each of the rooms that require heating, there will be one or possibly more radiators. Radiators must always be free of air and full of water in order to function well.

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Radiator operation

If you notice a cool spot on the radiator, particularly towards the top, it could mean that air is trapped inside. An air release vent on the radiator allows you to release the air using a special air vent key.

Releasing air should take place when the radiator is cold.

If you have a sealed heating system (one without tanks in the loft) then make sure that you know how to check that the water in the system is at the right pressure and how to top up the levels if it’s not. Please note that it is most important that your installer has instructed you on how to do this, or visit our You Tube channel for guidance.

Radiator performance

More often than not, radiators are sited underneath a window so that the warm air that they generate heats the colder air coming in through the window. A radiator will not perform as well as it should if curtains cover it or if shelves are fitted above. Putting furniture or tables in front of a radiator will also affect your comfort.

Even heat

Radiators should all heat up at the same even rate. To ensure that they do, your installer should have ‘balanced’ the system. This is achieved by adjusting each radiator’s lockshield valve, which regulates the water flow.

Turning off radiators

In a balanced system, individual room temperatures depend on all the radiators working at the same time. If you decide to turn off radiators, for example in spare bedrooms or rooms that you rarely use, you might find that rooms adjacent to those have a slightly lower temperature.

Watch how to top up your system at

Thermostatic radiator valves

The radiators in your home should ideally be fitted with thermostatic radiator valves (TRVs). which will enable you to control the individual temperature of each room They can be adjusted to suit the comfort levels you want and provide a simple way of reducing running costs The higher the number shown on the TRV, the hotter the room should get, up to a maximum of around 22C.

It is important to make sure that the area around a TAV is kept clear and is not blocked by furniture or curtains so that It can accurately detect the room temperature, Don’t be too concerned it the whole of the radiator is not as hot as an uncontrolled radiator. as it’s likely that the room is up to temperature and the TAV has temporarily shut the radiator off, Please note a TPV should not be fitted on a radiator in the same room as a room thermostat.

Maintaining radiator valves

To prevent TAVs and on/off radiator valves from sticking. turn them a little by hand every 2-3 months, It’s also important to check that the plastic tops on all valves are always in position and are not cracked or damaged so as to prevent accidents. Take care not to knock valves and pipework when vacuuming or cleaning floors to avoid damaging them.

Radiator removal for decorating
When decorating a room it can be more convenient to remove the radiator from its brackets allowing youu to paper or paint behind it more thoroughly. Usually this means isolating the two valves either side of the radiator and opening the union nut connection which will allow the water in the radiator to be drained into a container. The radiator can then be removed. Replacing the radiator after the work has been completed requires tightening the union nuts back to the radiator valves and then turning the valves back to where they were previously set. If the boiler is a combi and is run on a sealed system, the system will need re-pressurising. See our YouTube channel for guidance.

Underfloor heating
In a modern, well-insulated property, underfloor heating can act as the primary heating source and, in most cases, no other space heating method is required.
Underfloor heating operates with lower water temperatures than traditional radiator systems. This makes it the perfect complement for ground source and air to water heat pumps.
The low return water temperature of underfloor heating also makes it suitable for use with condensing boilers, ensuring they remain at their optimum efficiency, with significant energy savings,

Frequently Asked Questions

Why does so much white steam come from my flue?

If you have had a boiler installed since April 2005, it will be a high efficiency condensing type. Condensing boilers operate more efficiently than non-condensing ones as they extract more heat from the flue gases. In certain weather conditions, particularly when it’s cold, the temperature of the flue gases may drop and you may see a plume – a misty vapour – coming out of the flue. This plume is perfectly normal and means that the boiler is operating efficiently.

What sort of shower should be run off a combi boiler?

Because combi boilers produce hot water at mains pressure they are compatible with either a mains pressure balanced or thermostatically controlled shower.

In contrast, when a regular boiler and cylinder has been replaced with a combi boiler, any existing shower should be examined for suitability. This might be a pump assisted power shower for example, which is designed for mv-pressure systems and it may need adjusting or replacing.

Should I have a water softener fitted to my boiler?

Water softeners are now commonly used, especially in hard water areas around the UK.

With a condensing boiler, if you intend to use a softener unit you must remember that due to the change in the pH level, it would be unwise to fill your central heating system with such water as this could reduce the lite of your central heating and pipe work.

It is wise when adding water using the filling loop to your condensing boiler, that this is fitted prior to the softener unit.

It is acceptable for water supplied into the boiler for hot water from taps to be softened water, This will have no negative effects.

What happens if I suffer a power cut?

In the event of a power cut, a digital programmer will normally retain its settings for a set period depending on the model. A mechanical analogue timer with a clock face will stop when the power goes off, so when the power is restored you will need to reset it to the correct time. Once the timer has been reset, the boiler will operate as normal.

What happens if I run out of gas or oil?

With a natural gas-fired boiler you are connected to the mains gas supply line, so unless the gas line is interrupted tor some reason it’s unlikely that you will ever run out of gas. If you have an LPG or oil-fired boiler, you will need to order LPG or oil as and when required. Keep an eye on the level of fuel in your storage tank and make sure that you order supplies well in advance of it running out. If you completely run out of LPG or oil, air will need to be removed from the fuel supply line that runs from the tank to the boiler. It is always recommended that you ask your installer or service engineer to do this before you use your boiler again.

How do fill my system?

If you have a combi or system boiler, which are both sealed systems, there is likely to be a water pressure gauge on the front. This should be at a setting of around 1 bar whilst the heating is off, When the boiler is operating, the gauge will usually rise to bar or more and when the system cools down again it should return to around 1 bar.

If the gauge has dropped below the 1 bar level there is likely to be a small leak in the system and the water pressure will need to be topped up with mains cold water. You will only need to do this if you have a sealed system boiler.