Your first job is to identify your system.
If I asked the fuse second to left has blown do you know what itâ€™s for you would quite rightly ignore it.
So is it a combi boiler and if so what make and model? And what size piping.
If not combi what system is it running. Closed or Open. C, W, Y, or S plan. What valves if any are fitted and what pumps are fitted.
Central heating is improving every month, Sterling engines that also produce electricity, New heat exchangers where the hot water stored is central heating water and domestic hot water is instantly heated as it travels through the heat store with secondary heat exchanges for solar panels or immersion heaters connected to photo volcanic cells. Even heat pumps and chilling units with forced air radiators. In some cases controlled by mini computers. Even the boilers have moved on from the original on/off boiler to the variable out put three stage condensing boiler where a heat pump extracts the last little bits of heat from the exhaust system.
And as yet I have not left gas fired. As we move to oil again we have the oil engine where heat is extracted while cooling the engine and the electrical power may be used for other domestic uses or for under floor or ceiling heating systems.
There is no such thing as a standard system, even the combi boilers change make to make in the way it is all controlled. And are available in both open and closed systems.
The fuse by the way controlled the cig lighter in my car and as a result my lap top went flat as the inverter stopped working!!!!
OK - here goes. Open system (S plan i think)
Boiler is Myson Appollo, Grundfos pump, type UPS 15-50x18. Two x 2-port valves.
I have a cellar beneath the rear of the house so everything is readily accessible.
With HW only on. Heating return pipe is hot. Manifold with microbore returns from rear house radiators feeding into this are cold. Feed pipe beyond heating valve is cold. (Hot) Return pipe dissapears towards the front of the house and is not further accessible.
Front radiators heat up from return side - return side very hot, feed side less hot.
I agree looks like S plan. With micro bore chances of thermo siphon are very low especially down stairs. I would have expected faulty motorised valve may be not fully turning off. Maybe htg engineer has some advice sorry can't help much.
I'd still be looking at valves and actuators, is the valve opening and closing fully ?
Remove the actuator head from the valve and turn the valve manually to off, if the radiators cool down it is either the valve is stiff and the actuator cannot turn it fully, or the D shaped aperture in the actuator can become chewed and may be slipping on the spindle.
How long have you had this system ?
how long has this been a problem ?
any alterations or repairs lately ?
Pump in the right way ?
The radiators can only heat up if the water can circulate, so the 2 port valve cannot be closing fully.
Ok, if you'd said it had always been a problem in your original post I would have said:
If the valve and motorised head are ok - then it could be a problem with the pipework, where to start I don't know as I don't know the set up of your system or the layout of your house, best bet would be to get an engineer out - impossible to help more without seeing the installation.
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