Central Heating Problem - Lukewarm Radiators?

David firth may ne right. But it depends on the controls. Some utilise a three way valve which diverts the boiler flow to either the HW or CH, and some have two separate valves one dedicated to either HW or CH. Personally I much prefer the two valve system as it is more reliable and easier to deal with should a valve stick or the motor die.

Back to your problem. It may well be that the fault coincided with the engineer's visit. It would be very odd indeed if he caused it. These guys take some stick but at the end of the day they are about the best and keep up to speed by attending boiler manufacturer's courses.

The chances are you may get a different engineer anyway. There is nothing to prevent you viewing the work and asking to be fully informed about the fault. You are the customer.

p.s. If it were the pump, as others suggest, you would not get hot water.

When the water in the tank reaches the set temperature it will shut down the boiler which then can no longer supply hot water to the radiators.When you run off hot water and the temperature in the tank drops the boiler will then kick in pumping hot water to the tank and the radiators.

The most likely reason that this is happening is because of the central heating motorised valve.When you have the heating switched on at the programmer the valve will open up and activate a small switch inside.This switch supplies power to the boiler to fire up and supply the hot water for the radiators.These switches can go bad and stop the boiler firing up.The power for the pump will come directly from the boiler to operate the pump over run.

To make the system run a bit longer with out running off all the hot water,remove the thermostat from the tank and turn down the boiler thermostat about half way till the engineer returns.

As your water is working its most unlikely that the boiler is damaged. Its more likely that you have a problem with a zone valve not functioning correctly as you are only getting heating with the water running. Do you have two electrically operated valves in your airing cupboard ? Most of them have some method of checking as to wether they are open or shut, some are spring loaded and some motor driven open and shut so if there are 2 compare with both turned on and off. Only one valve is a little more difficult as I dont know what make valve(s) you have.If you can turn each part of the system on and listen in the airing cupboard at the valve(s)you can sometimes hear a slight whirring sound of the motor moving the valve and then you should be able to hear the pump start and the boiler will fire. If nothing happens on heating trial then its the valve. It may be possible to 'latch open' the valve and turn up the cylinder stat to fire the water then all will work. Be aware that the water will be hotter and will shut down when its hot so have lots of baths and do plenty of washing. Hope that helps.

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As the pipework is hot both sides of pump - is is clear that your boiler is firing up and heating the water (this means your thermostat and boiler are ok). The bleed valve to look at is the 1 at the 90 degree bend - after which the pipework is cold - - if the pipework at this point has air in it - the water will not pass it, and it will be cold. Alternatively, the previous advice to check your pump is valid - - as your boiler is heating the water, the pipework will get hot, because the water inside it is hot, but only in pipework upwards of the boiler. If your pump is not running the water will not circulate, nor will any pipework get hot if your bend has an air lock. it is possible the pump has seized, particularly likely if it has been running with air, rather than water in system (it's overheated). Try switching boiler off, letting pump cool - then re-start pump - a light tap on pump sometimes helps to free it at this point.

Yes it sounds like the circulating pump has failed. Locate the pump, unscrew the plug in the front of the pump and check to see if it is turning freely when the heating is turned on. If this had been a combi boiler, which i assume it's not, then i would have suspected the changeover valve from hot water to central heating had stuck in the hot water demand position.

The syncrone motor[small electric motor] inside the zone valve may have burnt out,this is not a diy job,you can by shifting the small lever on the side,open the valve manually but it will only heat the radiators if hot water is on as when opened manually it will not activate the micro switch,if the engineer only serviced the boiler this is just a coincidence,but he should have checked the system is working before he left.cant help more than this sorry.

Sounds like the three port valve. Look next to your copper cylinder. You will find a valve with three pipes going into it and a head with a wire going into it. On the head is a little lever, probably on the side. Manually pull this open fully. It should have a bit to hook it permanently open. If you call for hot water, your tank stat will activate the three port valve. It may be that it hasn't gone back properly.

As mentioned above, it could be something to do with the pump : but that doesn't seem likely.

Possibly a faulty 3 port valve which is failing to fully open in the heating only mode.

Sounds as if you have air in the system.Turn off all the radiators except one.Run the pump for half hour then vent this rad.Go around the entire system doing this. Boring but it usually works.

Why do you have both boiler and a tank ?

Seems odd to me. I'd ask him about that, also to check the pump and make sure the therostat is set to a decent temperature.