Boiler not firing for central heating

[TheHogness]

Well it's getting cooler & I've discovered the central heating is not working. I thought it might be the pump (Grundfos 15-50) as it was old & v noisy, so I replaced that Saturday which turned out to be a saga with leaking valves & unable to find drain point for central heating Anyway pump is now replaced OK. Boiler fires for hot water (eg if thermostat turned up on hot water cylinder) but not for central heating (if room thermostat turned up). Upstairs rads get warm/hot when hot water is on but downstairs rads cold (downstairs is microbore).
Bolier is glowworm fuelsaver 55F
Central heating thermostat is in downstairs hallway
Central heating pump replaced with new.
Rads bled, header tank emptied, cleaned & new inhibitor added.
There is a silver box 'switch' thing (Honeywell) - valve control?? above the pump which has a slider switch manual/auto which I have put on both settings & doesn't seem to make any difference. I have a spare one of these from when there was a suspected fail a few years ago (turned out it was blown programme control) so could try replacing it if it's not too difficult.
Thanks for any advice/tips before I call a plumber out. Cheers. Dave

 

[TheHogness]

After reading some other posts regarding these motorised valve controls, I have checked mine & there is no resistance on the slider switch (auto/manual) so it moves freely between the two settings if I push the slider, so I think maybe it has broken?? I think I can try replacing the motor (Honeywell) without replacing the 3 port valve?? & if that doesn't fix it then replace the 3 port valve itself??
Grateful for any advice /guidance, thanks.

Dave

 

[kevplumb]

turn both hw/ch on

turn cyl stat down does the valve move / make noise

 

[TheHogness]

Thanks for reply.

No the valve doesn't appear to make any noise, neither does the motor.
If I turn the cylinder stat up the pump starts but nothing from the valve/motor appears to be going on.

 

[kevplumb]

valve has to be your first port of call then

 

[TheHogness]

Is it worth swapping out the Honeywell motorised unit first before changing the 3 way valve? Or you think valve has seized which has killed the motor?

Thanks

 

[kevplumb]

if its the one with a dimple on the cover its a drain down

 

[doitall]

if its the one with a dimple on the cover its a drain down

Are you sure

 

[kevplumb]

flamin knew i was wrong can never remember till i see em

 

[TheHogness]

Hello kevplumb/doitall, yes it has a dimple on the top, I think I can just remover the cover to get at the fixing screws, remove & then bang a replacement on & see if that will turn the valve

 

[doitall]

If it has 4 screws don't remove the head.

If it only has two screws carry on.

 

[kevplumb]

check the valve is free while you have the head off

 

[TheHogness]

Thanks chaps, I'll take the cover off & check.

 

[D_Hailsham]

The valve can stick for two reasons: electrical and mechanical.

Turn of the electricity to the complete heating system (setting the programmer to HW OFF and CH OFF is not enough. If there is resistance when you move the lever from AUTO to MAN, the problem was electrical and this should have cleared it.

If the lever is still floppy the problem is mechanical - the ball of the valve is sticking. Remove the actuator box and you will see the valve shaft. Try turning this with a pair of pliers (it only rotates about 20 degrees). If it will not move try a small amount of WD40. If very stiff, you will have to replace the valve.

PS the lever should be normally at the AUTO end. MAN is for filling and emptying the system.