Frequently Asked Questions

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.

What is a combi boiler?

Combination boilers known as ‘Combi boliers’ provide central heating and hot water without the need for a separate tank to store water; hence you can easily tuck them away under the stairs or in kitchen cabinets.

Heats water instantaneously on opening a hot tap, so there is no need for a storage cylinder. This is the most popular type of gas boiler in the UK, now found in around 70% of homes.

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.

What is a system boiler?

A system boiler is just like an open-vent gas boiler, it works on the same principle of stored hot water. However, many of the major individual components of the heating and hot water system are built into a system boiler, which means that installation is quicker, neater, easier and more efficient.

Secondly, the hot water is pumped from the system boiler through the heating system to the radiators and hot water cylinder, resulting in a fast response and more economical running costs. The system boiler removes the need for a feed and expansion cistern.

What is a regular or open vent boiler?

Regular gas boilers or known as ‘Open Vent Gas Boilers’ are the heart of most old-fashioned heating systems. They provide heat for radiators directly and produce hot water which is stored in a separate hot water cylinder. The cold water is normally supplied by a cold water cistern, usually in the loft above the boiler (gravity feed) and there is also a separate expansion cistern.

These arrangements take up much more space than a combi boiler system, but because there is a large tank of stored hot water you can use several taps at once. This makes this type of system more suitable for larger houses with two or more bathrooms.

Unless a hot water cylinder is very well insulated it usually loses heat into its surroundings, thereby wasting energy. And the amount of hot water you can use is limited by the size of your cylinder.

For instance you might run a bath, and then need to wait for the boiler to heat up the water in the cylinder again before you can run another.

What is a programmer?

Programmers allow you to set when the heating and hot water come 'On' and go 'Off' again. By installing a programmer, and heating your home and hot water only as and when necessary, you will save energy and money.

What is a room thermostat?

A room thermostat constantly measures the air temperature of a space and can be set to whatever temperature suits you best. They are usually in halls, stairs or landing areas to sense the temperature of a home's main living spaces. When the temperature falls below the setting, the thermostat switches on the central heating; once the room reaches the set temperature, the thermostat switches the heating off. Please note that the timer or programmer needs to be switched on for the thermostat to work.

What is a programmable room thermostat?

A programmable room thermostat lets you choose the times you want your home to be heated and the temperature you want it to reach while it is on. In other words, it allows you to heat rooms or the whole house to different temperatures in your home at appropriate times of the day and week. And again, by heating your home and hot water only as and when necessary, it can save energy and money too.

What is a cylinder thermostat?

A cylinder thermostat keeps a constant check on the temperature of the water in a hot-water cylinder. It switches the heat supply from the boiler on and off as necessary to keep the water at a set temperature. Installing a cylinder thermostat could save you up to £20 and 110kg of CO2 a year.

What is a thermostatic radiator valve (TRV)?

TRVs sense the air temperature around them and regulate the flow of hot water entering the radiators to keep a set temperature in a room. Again, they can help you save money and energy - by allowing temperatures in some rooms than in others, and to turn off the heating in rooms that aren't used. In the majority of cases TRVs can not turn off the boiler when the whole house has reached the right temperature. To do that, you will need a room thermostat as well. Radiators in the space containing the room thermostat should not normally have TRVs. But if they do, you should keep the TRVs on their highest possible settings, and set the room thermostat to the required temperature instead. By installing TRVs, you could save around £10 a year and around 45kg of CO2 a year.

Hot advice - programmable thermostats, room thermostats and TRVs all need a free flow of air to sense the temperature. They should not be covered by curtains or blocked by furniture. Nearby sources of heat such as lamps could also stop them from working properly.

Why is my radiator cold at the bottom and hot at the top?

This usually means you have sludge build up in the bottom of the radiator. This can be resolved by power flushing the system. However, before taking any action we recommend that you seek our expert advice totally FREE.

Why is my radiator cold at the top and hot at the bottom?

This usually means that there is air trapped in the top of your radiator. You may want to try to bleed the radiator to release the air. However, we suggest that you have your central heating checked by an expert in case there are any underlying system problems.

Why are some of my radiators hotter than others?

This usually means that your central heating system is incorrectly balanced. This results in the hot water not flowing evenly to each radiator. We suggest that you have an expert check your central heating system.

HDM Heating is committed to providing our customers with the best quality service and products. We are also equally committed to reducing our impact on the environment so that our clients can reduce their carbon footprints at the same time.

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