central heating

[josieann]

CAN ANYONE ADVICE PLEASE

My central heating pilot light went out I called an engineer who said that the condensor had gone he replaced this but then found the  pilot light still would not stay on so he changed the part that keeps the pilot light on , the gas flow unit I think it was called.  This seemed to work but i then found the burners where not turning off hence the water and radiators where getting far to hot.    Gas engineer could not find reason why this was happening because the thermostat seemed to be working ok.   Another gas engineer came out and found that the thermostat did not fit flush into the tube in the boiler so this was recording cold instead of the proper heat.  Problem was the original installers had fitted this in by a screw to make the thermostat touch the metal to give a reading to the thermosta.   Problem I have now is although the burners are now turning on and off the radiators are still getting hot on the low setting.  Does anyone know what the problem is. 

[landie]

Could be that your thermostat is in an inappropriate position and is not measuring the air space you are living in, or it may not be working at all. Check firstly, however, that your timer for the circulation pump is not in the permanently 'on' position, (should be set to Auto).

[KARL]

The symptoms are consistent with a faulty or malfunctioning zone valve - assuming you have one (most modern systems do). These devices are energised from the thermostat (in this case the "room"-stat) and in most common models a low energy motor within the actuator (box bolted onto the simple valve)turns the valve to open and at that point a micro-switch closes, feeding power direct (separate from the thermostat) to the pump and boiler. When the thermostat clicks off the actuator mechanism is supposed to close the valve again and switch off the power to he boiler/pump. If either the valve sticks in the open position or the micro-switch remanis (faulty) closed, then power will continue to feed the circulation. Since circulation still takes place to the radiators, the valve is at least partly open. Find the zone valve - you may need to replace the actuator (usually removable and replaceable). Good luck

[josieann]

Thanks Karl for your reply gives me something to work on.  From what you describe does this mean there is a problem with the pump.  My system is 18 years old.  Fitter tells me it is still in good working condition and is baffled to what is wrong with it. He has eplaces the thermostat.thermo coupling and something to do with the pilot. It is truning on and of now but the radiators are far to hot even though it has been set at a low reading. l

[KARL]

Since the circulation is (I assume) reaching even the most distant radiator, the pump is doing what it is supposed to do. I know the symptoms because I have had exactly the same in my 31 year old system, several times - zone valve actuators are disappointingly prone to failure (sometimes as early as within little more than a year from new). But they are readily obtained and relatively easily replaced. Find yours and post the type (two port or three port, and make - there may be two, one for CH the other for HW) and I will see if we can work through a check on its function via this thread, if you are interested. Bear with me, I may take a few days to respond each time.

[josieann]

thanks karl i will endeavour to find wherethese are