No Heating without Hot Water...

[CarrierBag]

I am hoping someone may be able to shed some light on a heating problem I have.

I moved into my new home six months ago. As winter set in, I noticed an annoying problem with my heating system. The thermostat on the boiler appears to override the central heating. To explain: the room thermostat will be on but, once the boiler has reached its target temperature, will shut everything down, including the heating.

I can get the heating to switch on again only by turning the thermostat on the boiler up!

Any pointers as to what may be causing the problem would be greatly appreciated.

[ALAN]

This is one of the best replies I had when faced with the same problem. I was lucky to be able to switch the control unit from water to heating a few times and it released the stuck valve. Try that first before calling for help. This is the reply I got from Jim. Good luck. Sounds a bit like your 3 port valve could be stuck in hot water mode.

If you switch from all off to heating only, can you hear the valve powerhead motor running?

Does the boiler light with the just the heating on?

There's a couple of microswitches in the valve power head. When heating and/or hot water is called for, the powerhead motor turns the valve to the appropriate position, and in doing so operates the microswitches.

If the powerhead either can't turn the valve (because it's jammed), or has burnt out, the microswitches don't get operated, and the pump/boiler never get the signal to pump/light.

You can usually buy either a new powerhead on its own, or a whole new valve & powerhead together. If the valve is jammed, or even a little sticky, the powerhead motor can/will eventually burn out. In which case it's better to replace the whole thing - a new powerhead on an old valve will probably burn out in the same way.

Replacing the valve means draining your heating system down. The powerhead contains mains voltages. If you're not absolutely sure what that implies, suggest you get a plumber to fix it

Jim

[JimNoble]

I moved into my new home six months ago. As winter set in, I noticed an annoying problem with my heating system. The thermostat on the boiler appears to override the central heating. To explain: the room thermostat will be on but, once the boiler has reached its target temperature, will shut everything down, including the heating.
I can get the heating to switch on again only by turning the thermostat on the boiler up!
Any pointers as to what may be causing the problem would be greatly appreciated.

It's normal for the boiler to stop heating the water once it's up to temperature :wink: But the pump should keep running as long as the room thermostat is calling for heat. Is the pump stopping as well?

What sort of heating setup do you have? This may help in identifying what you have:

http://www.gasman.fsbusiness.co.uk/f...ed_systems.htm

Jim

[sunbeam]

The room thermostat is on as efficient as where it is placed.There maybe nothing wrong with the sysyem,only a poor sited room stat.

[CarrierBag]

Gents, thanks for the quick replies.

Jim, many thanks for posting your solution. It was only after posting my problem that I came across your thread. As you suggested, I ran through the procedure of switching from HW to CH in an attempt to free up the valve but I noticed the valve was moving freely. However, I think I may have an electrical problem rather than a plumbing problem.

As instructed, I started the system in CH mode, however, the paddle switch moved to the B position marked HW. I then switched it off again and started the system in HW mode. This time, the paddle switch didn't move at all and stayed in what I presume is the open position. Once again, I switched it all off, placed it in CH & HW mode and switched it on. If my understanding is right, the paddle should have remained where it was but again moved to the B (HW) position. 8O

As to your second post, it is a Y plan setup I think as it seems to be the only one with a three way paddle valve.

The thermostat is placed fairly near the kitchen but nonetheless, it 'clicks' on when turning it up to the desired temperature but no action from the pump until the thermostat on the boiler is turned up.

Hunting around in the airing cupboard, I found an old 3 way valve in there. I can only assume the previous owner replaced it thinking it was faulty.

Do you know of any websites that explain how the motor on the paddle switch should be wired up?

Thanks again.

Jason

[JimNoble]

Could be a DHW priority system (ie if hot water is called for, send all the boiler output to the cylinder, even if the heating should be on).

Also, it's hard to tell what the valve is doing sometimes - there's a spring in there that returns the valve to position A, and the lever doesn't act as a position indicator.

http://www.diyfaq.org.uk/plumbing/pl...e2.html#valves

It sound like it's doing the right thing though.

You say that the heating shuts down when the boiler reaches temperature - do mean that the valve operates and the pump stops running?

The pump should run so long as the heating is set to be on, and the room thermostat is calling for heat (and/or the hot water is on and the cylinder is calling for heat).

I can't think of a way to mis-wire the valve that would cause it to operate when the boiler thermostat switches.

Is your central heating controller part of the boiler or separate? (Often in or near the airing cupboard if separate)

Jim

[CarrierBag]

'do mean that the valve operates and the pump stops running?'

That's right, the pump seems to be on the same circuit as the boiler. When the boiler is on, the pump is running (regardless of the thermostat downstairs) and vice versa.

On closer inspection, it would seem that the thermostat downstairs is completely redundant as it doesn't appear to control the heating pump at all. As a test, I set it to CH only and turned the room thermostat to maximum but still this did not engage the heating pump.

'Is your central heating controller part of the boiler or separate?'

The Sunvic central heating controller is separate.

Thanks for providing info on the wiring. Let me know if there is any further info you may need to diagnose our heating gremlin.

[foxgeorge]

The boiler is the most important part of a central heating system. most boilers have a thermostat to control the temperature of the hot water flowing from pipes to the radiators. The correct setting of the boiler thermostat is High in the winter and Low in the summer.Its important to realise that the level of control you have over your heating and hot water is due to a combination of the plumbing system and the programmer.