Central heating gone berserk. Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Lou]

The system must be around 25 years old. It consists of an indirect cylinder with pump, motorised valve, cylinder thermostat, room thermostat and a timer control.
The problem is with the room stat not calling for heat the pump is running and the boiler keeps firing up and the radiators get hotter and hotter. Turn off the timer controller, no change, turn off the boiler and the pump keeps running. Cut the power to the heating circuit and turn it back on and every thing seems normal again. The problem seems to be as if something becomes stuck on. Any ideas anyone?

[ALDA]

LOU,

I WOULD START AT THE MECHANISM IN THE ROOM THERMOSTAT.

SEEMS LIKELY THAT IT MAY BE THE BIMETALIC SWITCH IS FAILING-MAYBE CORROSION/CONDESATION OR SIMILAR.

WORTH A QUICK LOOK UNDER THE COVER!

ALDA.

[muttley]

[quote="ALDA"]LOU,

I WOULD START AT THE MECHANISM IN THE ROOM THERMOSTAT.

SEEMS LIKELY THAT IT MAY BE THE BIMETALIC SWITCH IS FAILING-MAYBE CORROSION/CONDESATION OR SIMILAR.

WORTH A QUICK LOOK UNDER THE COVER!

ALDA.[/quote]
Also your motorised valve could be a problem,get it checked at the same time :wink:

[ericmark]

I will guess at micro-switch stuck in motorised valve! The thermostat works the valve then the valve works the central heating although the diagram only shows one switch in reality there are more like three as to how to test sorry took me ages as I was completely thrown by it not following the diagram hence I remember the problem.

[Lou]

Thanks all for your response, I’ve checked the room thermostat and it all looks fine. I did check it when the pump was still running on and every thing else was switched off and you could hear the switch clicking on and off as the dial was rotated, it made no difference. The motorised valve looks the likely culprit but could it power the pump direct when every thing else is off including the timer control?

[ericmark]

On the simple Y wiring if the timer is off so is everything else. But many boilers also have a feed to boiler which in turn feeds the pump to allow it to cool down.
The orange wire from the motorised valve feeds the pump and boiler and also connects to the cylinder thermostat.
There are other systems as well as Y the C system uses thermo-siphon for the hot water here there is a feed to the boiler direct through the valve without going through the timer but this would not unless there was a fault with motorised valve allow pump to run.
There are also W and S systems the latter allows zones and the former gives either hot water or central heating not both. The Y and C plans allow both.
All have valve/s and pump, indirect cylinder, cylinder thermostat, and room thermostat and timer. The Y system will not allow you to select central heating without hot water if I remember right. The programmers have switch and turn buckle which change them from 16 to 10 program setting. But sometimes they are not set correct anyway. The valves are different Mid position are only used with Y plan so if you can read the part number on valve and match it on web sites to find what type then we should be able to work out which plan is being used. Three port valves are used on Y and W and two port on C and S plans. I have got diagrams of C and Y on my web site but we are not allowed to give links. Starts www has same name as I log on here with and is with talktalk.net maybe you can find it?