The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.


Problem solving central heating 1

For problems relating to sealed systems, seek the services of a professional heating engineer.
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Cold top section of radiator

bleeding a radiatorThis is usually an indication that air has got into the system somewhere and has become trapped. Air in a radiator will rise to the top forming a pocket stopping the hot water from getting to that part. This can be released, but remember to turn the heating off first. Now, armed with a rag beneath, use a radiator key to slacken the air bleed valve which is at one end towards the top of the radiator. There will be a hissing sound as the air comes out. As soon as water begins to flow, close the vent again and wipe away any water.

Take care not to get scalded – the water may be pretty hot.
The heating can then be switched back on.

Some systems have an automatic air release valve fitted. This usually has a small red top which should be slack to enable the air to escape.

Radiators should not need frequent ‘bleeding’. If they do, air is getting in and this should be sorted out by a professional heating installer

Cold bottom section of radiator

This is a sign of rust and sludge build up which is sitting in the bottom of the radiator. Following the guides on removing and refitting a radiator, take the radiator outside and flush it through with a hosepipe. If you have the radiator standing on end, you should be able to flush out most of the sludge.

Remember to carry the radiator upside down so you don't get sludge dripping on to your carpet.

With an open vent system, you may also consider using a proprietary heating system sludge remover. Iron oxide which has built up in the system is broken down and dispersed through flushing. This will mean adding it to the feed and expansion tank and, a few days later, emptying and refilling the system.

Follow the manufacturer’s instructions.

Treating the system with a sludge remover will maintain the efficiency of your heating system conserving fuel and saving you money. Stick to the well known brands like Sentinel and Fernox. Personally, I'd go with Sentinel X400 and after afterwards add X100 to protect the system. A litre of X400 should be enough for a system with up to 10 radiators.

Upstairs radiators cold

This is most often an indication that the feed and expansion cistern in the loft has run dry.

This should not happen and indicates another problem which needs to be sorted.

It’s probable that the ball valve is not operating correctly. It may have jammed or be obstructed. Clear any obstruction or replace worn parts. Remember when refilling and adjusting the ball valve that there must be enough room for the water to expand when the system heats up. Therefore, when the system is cold, there should be just enough water to make the ball to float and switch off the water coming in.

Downstairs radiators cold

This is an indication that the pump has packed up. Have it tested and, if necessary, replaced.

All radiators cold or not very warm

This again is an indication of the build up of rust and sludge. See ‘Cold bottom section’ above.

Radiators cooler in one area of the house

This tells you that the radiators are not properly balanced. The nearest radiators to the boiler are taking more than their share of the hot water from the system. See page on balancing the system.

Warm radiators upstairs when the heating is off, and hot water is on

If this happens, it is probably because the check valve on a gravity fed system has failed. In a gravity fed system, the hot water cylinder is heated by water from the boiler which flows due to the gravity and not a pump. To prevent the water also heating the radiators when the heating is off, a check valve is fitted. If this has failed, the radiators upstairs will begin to receive some of the heat.

The valve will need to be replaced by a heating engineer.

No heating or hot water

Make sure that the power supply is on and that a fuse hasn’t blown. Remember, if a fuse has blown, you should always rectify the cause first.

As always, take great care with any electrical inspection or work. See electrics safety

Check that the gas or oil supply has not been turned off inadvertently.

In the case of oil, check that you actually have some oil in the tank by reading the gauge.

Check that the programmer is in the on position and that the thermostats are turned up high enough.

Check that the pump is running. If not, get a heating engineer in to investigate.

Check that the pilot light is lit. If it isn't, follow the details for relighting in the boiler manual.

If none of these solve the problem, it’s time to call in a heating engineer.

Feed and expansion tank overflowing

If the ball valve is not closing off the water supply properly, the cistern will continue to fill and water will come out from the overflow pipe. The usual cause is either a poorly adjusted valve or a worn washer. These can both be remedied in a similar fashion to the ball valve of the cold water storage tank.

Problem solving central heating 2

T&S Heating Limited