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
This 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
- Radiator - removing
- Radiator - refitting
- Balancing a central heating system
- Ball valve
- Central heating systems
- Draining down a system
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1) Micro switches in motorised valves. With the older systems the thermostat does directly control the boiler but instead opens the motorised valve. This in turn starts the central heating boiler. Sometimes manually latching the valve as one would do to bleed will get central heating running again but this means the radiators will heat up in Summer so only temp fix.
2) Balancing radiators. In the old days as stated on the article out of balance radiators would mean some don't get hot. But with the newer systems the thermostatic radiator valves will close the supply to radiators in warm rooms so diverting the supply to cold rooms so even with all the lock shield valves wide open the system will in the end heat all radiators.
However unlike the old boilers which only monitored the temperature of the water leaving the boiler the new boilers also monitor the temperature of the water entering the boiler in order to keep it cool enough for condensing to take place. The boiler does not simply switch off and on but varies the flame height so supplying just enough heat.
While running this works fine. As each radiator becomes cool the thermostatic valve opens allowing hot water into it and soon after it becomes hot the valve will close again controlling each room independently.
The problem is when the system has been turned off. If the lock shield valves are wide open as the system starts it pushes all the water through the easy radiators. These quickly get hot and hot water is then returned to the boiler which in turn turns down the flame height. So until those first rooms have got warm the other rooms are not heated. In fact open doors can mean the other radiators never turn on. I have come across this with many houses. And since in the end the radiators do get hot it just takes a long time the occupant can be unaware there is such a simple to cure fault. They just think the boiler is not big enough.
There also seems a lack of up-dating with many plumbers and they still do things like leaving one radiator without a thermostatic valve.
Theory is on a hot day all valves are closed so when boiler starts the by-pass valve opens straight away sending hot water back to the boiler. With good boilers the software if the boiler runs for under a set amount of seconds extends the time before next run. Conversely if under set amount of seconds it will shorten the time before next run. So during the summer it will likely only start up 6 times a day which is wanted anyway to stop the pump from sticking.
But if too much water can go around the system then the boiler thinks it's colder than it is as the return time is exceeded. A small towel radiator likely will not allow enough flow to fox the system but a radiator in a hall etc will.
But because for years it was standard practice for the radiator where the electric thermostat is placed not to have a radiator thermostat it is still done today.
The whole idea of an electric thermostat is to stop cycling in the summer so should not be in coolest room any more but in the morning sun. So stopping the system from running when we are likely to have a warm day.
However unlike the radiator thermostat the electric one can also have a timer built in. On the old system this means you can set 4 different temperatures at different times of the day. On a new system when set to a high temperature it will never switch off and the radiator valves will do the controlling but when set to a lower temperature the house reverts to old pre-radiator thermostatic valve days and each room is controlled by the setting of the lock shield valve.
Although careful selecting of radiator sizes and trimming of the lock shield valve can work. In the main it doesn't and you get warm and cold rooms while set to low temperature. As one would expect one can get some real odd results which will also change according to wind direction and outside temperature.
Good central heating engineers can combine the two systems to very good effect. But a bad heating engineer can leave a house with a completely uncontrollable system. In the main to be fair it's the DIY man adding electric thermostats to a system designed not to have them.
As an electrician I get called to change a faulty electric thermostat realise what's wrong but lack the equipment to be able to adjust the system even if the house holder will pay for our time.
I have a digital thermostat with two inputs and can measure the differential between in and out pipes on a radiator. In the past I have tried to set-up a system. If starting from cold not too hard. But once house has warmed up the switching of all the radiators in the house can produce some very varied results. However get the heating engineer who is doing it every day and he works more from instinct than meters and can do in half an hour what it will take me half a day to do. I may do it 4 times a year he does it at least once a week and now I don't even attempt to set them. I give the house holder his number and accept he has a skill I lack.
So what I am saying even if you have read and understood all I have said. You can expect to spend two days tweaking the lock shield valves and even then wind direction and outside temperature can upset it all. If they will not call the guy then all I do is close a valve down on a radiator near the boiler and then slowly re-open 1/4 turn at a time until I feel hot water flow counting the turns. Then set rest to same amount. Not the right way but works most of the time and does not take too long.
