Radiator gets hot although thermostat is off

uklisa · 29 Sep 2007

Please can you help. We turned the heating on a couple of days ago and we have reaslied now that the heating will not turn off with the thermostat.

We have turned the dial to as far off as we can but still the raditors are hot. I have also tried turning flicking the switch on the dial in the airing cuboard which controls the time for the heating and water to come on. We normally have it on constant or there abouts but i have tried putting it onto water only and still the rads are hot.

What is going on?

MattChan · 29 Sep 2007

At a guess it could be a 3 port valve that has failed assuming your system has one! A T piece type thing near the pump with a wire coming out of it

It diverts the hot water to the heating or hot water or both.

If it gets stuck or fails then it might not be able to close off its output to the central heating.

uklisa · 29 Sep 2007

Not sure about that but there is a metal box looks like a HVAC from what i have found on the internet it has a wire coming out of it and it sits on pipes.

It is all the way on auto.

Any help?

MattChan · 29 Sep 2007

Does it look like this:

or this:

uklisa · 29 Sep 2007

The first one.

uklisa · 29 Sep 2007

Ill be back in about 10 - 15 mins, thank you.

uklisa · 30 Sep 2007

I am guessing looking at the picture of the top one i have the 3 port valve is this what needs replacing?

uklisa · 30 Sep 2007

What would happen if i moved it to man open? or moved the lever a bit to the middle? Would that help?

Space cat · 30 Sep 2007

That's a three port valve. The water from the boiler comes in through the middle pipe and is directed through either or both of the other two, one to the cylinder and the other to the radiators.

When it's working properly it will rest in the HW only position, closing off the flow to the radiators. A demand for HW starts the boiler and pump but the valve stays put. An additional demand for CH operates a small motor in that box which drives the valve against a spring to mid-position, opening both outlets. In a really quiet house you can hear it move. The HW demand is still driving the boiler. Now for the clever bit. Your HW demand goes off, and so does the boiler, but you still want CH. IF AND ONLY IF the valve is at mid-point, an extra wire from the controller - let's call it NotHW - drives it all the way over to close off the HW outlet AND a switch inside that box feeds power from the CH demand back to the boiler to start it up again. In all cases, the spring will send the valve back to HW only when all power is removed.

That's how it's supposed to work. Yours might be stuck in mid-position. That lever on the end is a manual opening lever. You use it to put the valve into mid-position for filling and bleeding but it can also be a useful diagnostic aid. If the valve is resting in the HW position you will feel resistance as you move the lever. That's the spring. You can also feel the valve moving back under spring pressure when you release the lever. If your lever swings freely, the valve is not in the HW position. Give it a try.

uklisa · 30 Sep 2007

The little metal lever move freely from auto to man open and back to auto.

John M · 30 Sep 2007

The screwfix man hasn't been has he ?

Space cat · 30 Sep 2007

The little metal lever move freely from auto to man open and back to auto.

Your valve is either stuck in mid-position or else it's being held there by an electrical fault. You should have some means of removing all power to your heating system; it might be an unswitched FCU. You'll know when you've found it because nothing will work. Does the valve close now?

uklisa · 30 Sep 2007

Sorry cant find a way of removing power here is my AC below, i have taking photos and stuck them together as best as i can. thank you

Space cat · 30 Sep 2007

That fused switch on the right next to the socket looks promising.

uklisa · 30 Sep 2007

Sorry to sound stupid so what shall i do?

switch the fused switch
Then turn the heating etc back on see if anything happens
If no power try moving the metal level on the T piece again?

Then what should i look for?

Thank you, I am female, web designer, Avon lady and like to DIY but never tried anything like this before.

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Radiator gets hot although thermostat is off

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