Boiler fails to switch off when CH and HW demand removed

[dbharrison]

I have a Worcester Bosch 18Ri boiler which was installed about 3 yrs ago. Recently the system pump failed and was replaced. I then noticed that the boiler and pump were occasionally coming on in the middle of the night(Temperature in loft about 50 degs F, too high for Froststat) even though there was no demand from programmer. The problem then got worse and the boiler now fails to turn off when a heating cycle has ended even though the programmer has switched both CH and HW demands to OFF.
The problem only occurs after the system has been running in CH only mode(HW only or HW+CH do not show the problem).
When the problem occurs I am left with about 130v on the orange wire to the 3 position valve and the boiler, which appears to be keeping the boiler on.
In this condition there is 230v on the HW OFF wire from the programmer (which is correct) and if this signal is removed either by disconnecting the wire from the programmer or by disconnecting the grey wire into the valve the 130v signal on the orange wire disappears and the boiler switches off.
I cant see where the 130v comes from or tell whether this is normal (although I don't see how it can be)
Seems a bit of a mystery
Any ideas gratefully received.
dbharrison

 

[Chalked]

Are you sure it's not just the boiler pump overrun?

 

[vern]

I have a Worcester Bosch 18Ri boiler which was installed about 3 yrs ago. Recently the system pump failed and was replaced. I then noticed that the boiler and pump were occasionally coming on in the middle of the night(Temperature in loft about 50 degs F, too high for Froststat) even though there was no demand from programmer. The problem then got worse and the boiler now fails to turn off when a heating cycle has ended even though the programmer has switched both CH and HW demands to OFF.
The problem only occurs after the system has been running in CH only mode(HW only or HW+CH do not show the problem).
When the problem occurs I am left with about 130v on the orange wire to the 3 position valve and the boiler, which appears to be keeping the boiler on.
In this condition there is 230v on the HW OFF wire from the programmer (which is correct) and if this signal is removed either by disconnecting the wire from the programmer or by disconnecting the grey wire into the valve the 130v signal on the orange wire disappears and the boiler switches off.
I cant see where the 130v comes from or tell whether this is normal (although I don't see how it can be)
Seems a bit of a mystery
Any ideas gratefully received.
dbharrison

If you are GSR post in the relevant area and I will tell you the answer easy one.

 

[dbharrison]

Yes quite sure. When fault occurs it is permanent.

 

[iiplumbing]

Sounds like the limit switch on the (or one of the) motorised valves to me.

I my case the pump keeps running although the boiler doesn't fire.

So a simple case of checking to see if the feed from the motorised valve stays live when operated

Hope this helps

Russ