Hot water comes on at Random - Potterton Suprima Boiler

[gdbarratt]

I have a Potterton Suprima 70 Boiler which for some reason the hot water comes on when no timer is calling for it to come on.
I have done the following:-
Replaced the thermostat on the hot water tank.
Put in a new Drayton electronic Timer unit.
Replaced the boiler PCB for the new redesigned one.

I now have no lockouts but every hour or so the hot water comes on for around 5 mins then goes off again.

I am very confused as to what may be causing this.

Any ideas - help would be much apreciated as I am having to resort too powering the boiler on and off at the mains.

[gdbarratt]

Just been running a few more tests and the hot water fires about every 10mins and runs for about 30/40 secs.

I have been through the manual and can find no reference to what can be causing this.

[screech]

the zone valve or mid position valve switch jammed on?

[gdbarratt]

[quote="screech"]the zone valve or mid position valve switch jammed on?[/quote]

How does a zone valve/diverter valve managed to call for hot water?

The timer is set to off for both HT and CH yet the HT comes on every 10mins or so, I am a bit confused as to how a motorised diverter valve sends an instruction to the bolier to fire up the HW.

Any advise would be much apreciated.

[screech]

the valve will have a permanent live so will be live whether the clock is telling it that it wants to be on or not, therefore the boiler will come on but go off shortly after as it's already up to temperature. so if it's got a stuck microswitch or jammed synchron motor (jammed open) it'll always be calling for heat and the boiler will always want to fire up.

[gdbarratt]

Thanks very much for explanation.
I remove Actuator off the valve for HW last night and it instantly moved to a new position.
I then replaced, manualy moving valve.
Reset heating and all was fine until this morning when the HW and CH came on (with timer) and then the CH shut down but HW kept going.
Went upstairs and lifted actuator again and it moved again, replaced and back to normal again.

So it looks like the Diverter Valve or Actuator is at fault so thanks for the tip.

Just now need to work out if the valve is stiff and needs replacing or if the actuator needs replacing.

[screech]

would've replied earlier but been away. if you can turn the spindle on the valve by hand it's fine, if you need a spanner then it's too stiff.

[screech]

it doesn't always work that well but you can spray the spindle on the valve body with wd40, leave it for a bit then turn it a few times with a spanner, spray a bit more, leave for a couple of mins, then another go with the spanner. if you can turn if by hand afterwards see how it goes.

[gdbarratt]

Thanks, valve was fine, purchased a new Drayton actuator on internet for £30 and fitted.
Working fine now.

Thanks for all your help.