Glowworm Space Saver mkII control issue

[timmel]

I have just moved house and now have a Glowworm Spacesaver mkII boiler with storage cyclinder (installed in 1986 apparently). The problem I have is that the boiler only fires when there is a demand to top up the hot water cylinder. i.e. when hot water has been used the boiler heats up hot water and the radiators fine, no problems.

But when the hot water cylinder no longer demands heating, the boiler stops firing to the radiators too (even though the temperature is well below the level sewt on the thermostat).

I have changed the thermostat and this doesn't sort the problem. The system seems to work fine when the water cylinder is being heated, but not when it isn't being heated.

Any ideas on the likely cause? Thanks. in advance.

 

[Hugh Jaleak]

Have you got any motorised valves?

 

[timmel]

Have you got any motorised valves?

I'm not sure, where would the motorised valves be?

I think the circulating pump is still going but it seems as though the boiler stops firing as soon as the hot water cylinder is full.

 

[Hugh Jaleak]

Motorised valves, there would be either one with 3 connections, or two with 2 connections, located just after the pump, possibly in cylinder cupboard. Brass body with pipes attached, and a silver or plastic head with a wire coming out.

 

[timmel]

Not sure from memory and I'm not back home until Friday evening. What have I to look out for then with these? Is there a tell-tale sign if these are faulty? Is this the likely fault in your opinion?

 

[Hugh Jaleak]

If boiler and pump are working, you have hot water, then its possible the heating valve isnt opening to let the water around the heating circuit. If you have the 2 port versions, they are powered open, spring close. If there is a problem it may not open as it should. Easy temp remedy if this is the case.

 

[timmel]

Perhaps the problem could be whatever sends the control signal to the motorised valves then? As when the hot water cylinder is being heated, the heating system operates as it should do. The only problem is when the water cylinder no longer requires heat. At this point, the radiators go off.

 

[Hugh Jaleak]

AFAIK (Mandate/D. Hailsham are the experts on workings of motorised valves!), the valve is controlled by signals from the appropriate stat. Stat calls for heat, so sends 240v to the valve to energise the motor. This opens the valve and then activates a microswitch which supplies the power to the boiler and pump in order for them to operate.

It is possible the valve is opening as per supply from stat but the microswitch is faulty thus not supplying power to the boiler. (Boiler will receive power from the hot water valve when required by the cylinder stat, and so also heating the rads, but when cyl stat is satisfied it shuts boiler down. Heating valve should continue to supply the power but doesnt.) Failing this it could be a fault in the actual wiring of the system. If it has never worked properly since you've been resident then unfortunately it can get complicated to resolve...

 

[timmel]

Thanks Huge Leak (sorry, I mean Hugh Jaleak!).

I am hoping that the cyclinder stat was just wired by a numpty and is therefore shutting off the whole boiler when the cylinder is full, rather than just the hot water valve. Failing that, sounds as though it could eb the microswitch that is causing the incorrect switching.

 

[timmel]

Any further thoughts on this issue or do others agree that it is likely to be motorised valves/microswitch problem or just terrible wiring from the installer of the cylinder stat?