Help Please - CH Only Comes On When Water Is Heating?

[punkrokka]

I've got a problem with my central heating .... it will only stay on while the hot water is heating up. If the tank water is hot the heating won't come on at all but if the hot water is being used I'll get heat. The CH won't work independently.

System is a Potterton Suprima Boiler with Honeywell wall thermostat, timer (ST6400C), Silver Box (V1073A 1039) & Tank Thermostat (L641A1039) controls. Pump is a Grundfos Selectric (59525600) set to III, Tank has a Sadia Water Heater on top.

So far I undid the large pump centre screw and turned the smaller inner screw left/right. The lever on the back of the silver box doesn't seem to have any resistance so I undid that to check if a spring had come loose but all looked ok. Moving the lever left to right is loose but it did click back once as if it was on a cog?

Can anyone offer any advice ?

Thanks

 

[gas4you]

Are you sure the 'silver box' is not a 4073A?

It will be this box that needs replacing. The microswitch has broken in it.

 

[punkrokka]

Thanks...probably is 4037A, the first part is scratched over.

What is it that this box does, or doesn't do in my case?

Are they easy to change for a novice & are they expensive to buy?

 

[kevindgas]

The microswitch has broken in it.

that is your answer - its cacked!!

best get a competant plumber in to change it (get an ACL/drayton one they are better as come in 2 parts - motor and body)

 

[punkrokka]

Cheers...all sorted.

Got a replacement 4037A (Prices quoted between £35-£95) and fitted it myself. Was told that motor could be changed for £12.50 but was too late.

Simple job....turn off mains, drain down tanks & tie up floats then it's just three like for like bolts and five wires to replace. Turn it all back on and bleed the rads. Worth treating the system to some descaler at the same time....I'd forgotton how warm it should be.

Definately worth a go yourselves.

Thanks for the help