Central heating motor stuck on?

[Roger465]

Unfortunately, I live in a Redrow house. This means, amongst other unpleasant things, that I sleep directly below the hot water tank, central heating motor etc. That, combined with the generally cheap and nasty construction of the house, means that you can hear individual atoms crashing around in the airing cupboard when you're trying to get to sleep.

When the motor bursts into life, as it’s mounted in the middle of several feet of completely unsupported pipework, you jump out of bed in terror, remembering stories of 50-gallon tanks full of boiling water (directly above your head) crashing through the ceiling and onto the people sleeping below.

So… last night, I went to bed, and the motor was rumbling away above my head. It shouldn’t have been, because the heating had been off for about 2 hours, and the hot water comes on in the morning. I went up to the airing cupboard, and found it happily spinning away, and pretty hot.

As with computers, I decided that a good plan would be to switch everything off and on again in the hope that something, somewhere, would reset. Unfortunately, being a computer engineer and not a plumber, I have no idea what “everything” might be. But I found a couple of boxes (below hopefully).

Moving the little lever carefully to the right and back again on the galvanised box had no effect – however, when I moved the one on the plastic box up and down again… it worked! The motor went off, and stayed off, and now everything seems to be working again.

Could anybody please tell me (a) what the two boxes actually DO, (b) if I need a new plastic one?

Thanks!

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• Roger465
• 14 Apr 2013
• 1

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• Roger465
• 14 Apr 2013
• 1

 

[ianmcd]

Both do exactly the same they are just different makes, they are called zone valves, one is for HW the other is for CH, basically they have a small motor and when you select that function the motor opens the required valve, once the valve is fully open it closes a micro-switch which brings on the boiler and the pump, it sounds like one of the micro-switches is sticking in the closed position when the valve returns, you may be able to replace only the actuator unit of the faulty valve depending on the model you have or you may have to replace the whole valve which is a much bigger job

 

[Roger465]

Thanks a lot for that. Just for my education (as I fix computers for a living, I’m the kind of person who just HAS to know how things work…), could you possibly explain a little more for me?

I guess there are two “circuits” (I mean pipework, not wiring) for heating and hot water? And when you say “select that function”, you mean that the timer downstairs turns the heating or hot water on?

If so, if I understand you correctly, electricity from the timer energises a motor in the valve (I assume they use a stepper motor rather than a simple solenoid as it’s a higher physical load), and that allows water to flow in that circuit. The valve opens first, then the micro-switch turns the rest of the kit on – if it turned these on too early, I suppose you’d have a pressure problem.

So if that lot’s correct (?) I assume the pump circulates water from the tank to the boiler, thus heating the water, when that valve’s open – and round the boiler and radiators when that one’s open. I think there’s only one pump, right?

Finally, I “cured” things by pulling the little lever on the zone valve – does that manually energise/de-energise the motor in the valve, or what?

Very very grateful for your advice – if anybody needs any computer advice, feel free to PM me

 

[Armo74]

You have what is known as an s plan, when the cylinder thermostat calls for heat it energises the motor which moves the valve over,when it is in the open position it activates a micro switch inside the actuator (the silver box on the side of the valve)which then powers up the pump and boiler. The same thing applies for the other valve but is moved when the room thermostat calls for heat. On your type of plan you will have a bypass valve which allows a flow of water through the boiler when the valves are closed in the event that the pump overrun kicks in. The manual levers are there to allow you to drain and re-fill the system.

 

[ianmcd]

Thanks a lot for that. Just for my education (as I fix computers for a living, I’m the kind of person who just HAS to know how things work…), could you possibly explain a little more for me?

I guess there are two “circuits” (I mean pipework, not wiring) for heating and hot water? And when you say “select that function”, you mean that the timer downstairs turns the heating or hot water on?

If so, if I understand you correctly, electricity from the timer energises a motor in the valve (I assume they use a stepper motor rather than a simple solenoid as it’s a higher physical load), and that allows water to flow in that circuit. The valve opens first, then the micro-switch turns the rest of the kit on – if it turned these on too early, I suppose you’d have a pressure problem.

So if that lot’s correct (?) I assume the pump circulates water from the tank to the boiler, thus heating the water, when that valve’s open – and round the boiler and radiators when that one’s open. I think there’s only one pump, right?

Finally, I “cured” things by pulling the little lever on the zone valve – does that manually energise/de-energise the motor in the valve, or what?

Very very grateful for your advice – if anybody needs any computer advice, feel free to PM me

You have the correct idea but the pump doesnt circulate water from the tank to the boiler at any time, when the DHW zone valve calls for heat the same water that goes through your rads is circulated to a closed coil of pipe inside your HW cylinder which heats that water, think of it as a radiator inside your HW cylinder and that is what heats the water that comes out of your taps , the two waters never actually meet

 

[Roger465]

the same water that goes through your rads is circulated to a closed coil of pipe inside your HW cylinder which heats that water

Sorry, I did know that bit – the moonshine distillers where I come from in Ireland use old hot water tanks in reverse, kind of thing – the alcohol vapour goes into the coil, and cold water is circulated through the actual tank – the moonshine runs out of the coil at the bottom.

But was I right about the lever on the side of the valve – does that manually make and break the circuit?

 

[stem]

Being a simple soul, I find diagrams assist my understanding. (If only that were possible with software...sigh) Heated water from the boiler is circulated via the pump to either the hot water cylinder, or heating, or both as required by the system thermostats and the programmer (programmer in this case being a timeswitch. Nothing to do with software). The valves open and close to control the flow.

As has been said, when the valve winds to its fully open position, it operates a microswitch that turns the boiler and pump on. However, the manual lever will not open the valve fully to the point of operating the microswitch.

It is fairly common for these switches to stick, so I agree with ianmcd's suggestion.

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• stem
• 17 Apr 2013
• 2