boiler problems

[iain_b]

Hi all,

I've got a British Gas boiler, Model 50F2 (made by Potterton).

When I try to put the radiators on - nothing happens. When I try to put the hot water on - both the hot water and radiators come on. The boiler is 7 years old and the problem has just started, is there something sticking?

Any help would be much appreciated.

Thanks,

Iain.

[Jim Alexander]

Not necessarily the only answer but the symptoms can be explained by a faulty heating zone valve, either synchron motor or microswitch.

Jim A

[Roger Mills]

It's unlikely to be a boiler problem per se. The boiler obviously works, or it wouldn't do anything when both HW and CH are turned on. The problem is likely to be in the external controls - motorised valves, thermostats, etc. What type of system have you got? Have a look at

and see whether your system conforms to one or other of the standard 'plans'. If you tell us which one, we'll tell you what to look for.

[iain_b]

Further investigation shows that the boiler doesn't even 'kick in' when the heating is switched to 'on' and if the boiler is running with the hot water on then switching the heating to 'on' will switch the boiler off altogether - is this more likely to be pointing to the microswitch?

Thanks, Iain.

[iain_b]

at

see whether your

Thanks Roger,

Further investigation shows that I've got the S plan system - I think. Also turning the heating to 'on' won't start the boiler and if the boiler is on with the hot water control, turning the heating to 'on' will switch off the boiler altogether, I'm confused.

Thanks,

Iain.

[Jim Alexander]

Firstly you need to post whether you have 2 x 2 port zone valves or 1 x 3 port. From your description of the fault guessing 3 port.

Jim A

[Roger Mills]

You ain't the only one!

Correctly functioning S-Plan systems will run the boiler whenever either or both HW and CH are calling for heat, and turning on one won't stop the other!

Has any work been done on the system recently - particularly replacing one of the motorised valves (or just its actuator)? I can't explain the symptoms unless there's a wiring fault, and even so, you'd have to be quite 'clever'[1] to produce this particular effect.

[1] The secondary switches on the valve actuators are supposed to be wired in parallel. To get this effect, you'd have to wire them in series *and* use the NO contact on one and the NC contact on the other!

[iain_b]

Hi Roger,

No work has been done on the system. I'm now totally confused - both the hot water and heating are in the 'off'' position on the controller, but the boiler is still working - I'm guessing that the controller's internal circuits are goosed and hopefully a new controller will fix things. It's a British Gas UP1 controller, any ideas where I can get such a thing - I take it it will be a Honeywell or similar re-badged.

Thanks,

Iain.

[iain_b]

Hi Jim,

There are 2 motorized valves in the system. Now the boiler switches on and stays on even if both hot water and heating are in the 'off' position - is it likely that the wall controller is faulty? It's a Britisg Gas UP1 controller, is this likely to be a Honeywell or similar and any ideas where I could get one?

Thanks,

Iain.

[Roger Mills]

No, there's a more likely explanation than a duff controller.

An S-Plan system works like this: The controller and room stat control the CH zone valve. The controller and cylinder stat control the HW zone valve. Each zone valve has a secondary switch in its actuator which is electrically isolated from the motor circuit, and which makes when the valve is fully open. These secondary switches have a permanent live input (independent of anything the controller or stats are doing) and their outputs feed the boiler and pump. [If you study the S-Plan wiring diagram in

you'll see what I mean]

If one of the valves sticks open (or if its secondary contacts weld closed) the boiler and pump will run even when everything is switched off. You need to have a close look at these valves!

[iain_b]

in

'll see what I mean]

Roger,

I checked the valves and the heating one was stuck, working it open and shut with a spanner and a wee bit of WD40 loosened it off completely, did the hot water one too for good measure. Everything is working properly now. Thanks very much for all your help - this central heating novice (could you tell?) was totally lost.

Cheers,

Iain.

[iain_b]

Jim,

System fixed, the heating valve was stuck.

Thanks,

Iain.

[The Natural Philosopher]

in

'll see what I mean]

Be advised that once they stick once, they tend to do so again with increasing frequency until they are irreperable.

Schedule a replacement for a quiet day next summer, and get the part in now in case you need t do it on an icy Sunday morning in winter..