Boiler runs but pump doesn't - central heating system.

[xert]

Hi all - hope someone may have had this problem before. Central heating with 3 way motorized valve - problem is that on any setting, ie heating on, water on or both, boiler will fire up assuming thermostats are turned up, however pump will not - consequently cut out occurs on boiler within a few minutes due to no circulation.
Have hard wired pump directly to mains to test and runs fine, however when wired in, both wires show live when tested with neon screwdriver. This fault ocurred this evening after running fine for a couple of hours.
Sems that the fault is that there isn't any voltage difference across the pump hence doesn't run.
Should I be looking at the three way valve as probable cause or elsewhere ...
Any help would be gratefully appreciated !
Xert.

 

[corgiman]

go on gissa a clue?

what boiler do you have?

 

[xert]

Hi - boiler is Myson Orion, valve is Horsemann Z322.

 

[corgiman]

cor blimey thats an old un

sorry I have very little experiance wif them so I will bow out now

 

[xert]

Thanks for looking in Corgiman - having checked more in the connection box where the pump, valve and cylinder are located, all of the terminals on the barrier strip (with the exception of earth of course) read live.

 

[corgiman]

but when you wire up the pump independantly it runs ok does it?

 

[xert]

Yep - runs fine. I'm pretty sure the problem lies in there not being a neutral return but can't seem to figure out the return path ! Is there a possibility the return could be via the room stat and the neutral could be lifted in there for some reason ?

 

[corgiman]

How is the polarity?

 

[Agile]

Yep - runs fine. I'm pretty sure the problem lies in there not being a neutral return but can't seem to figure out the return path ! Is there a possibility the return could be via the room stat and the neutral could be lifted in there for some reason ?

Clearly there is a neutral lost somewhere.

Clue blue wires!

Follow measuring from the chassis earth to the neutral inwards to the point where it becomes mains voltage.

Probably a neutral wire tightened up on the insulation instead of a stripped wire.

An easy fault compared with the one that took me three hours today!

I would expect to find it in 11 minutes starting with the covers off.

Tony

 

[xert]

Many thanks for your thoughts guys - I'm on the right track now looking for the neutral path.
Best regards.

 

[xert]

Thought anyone watching this post would be interested to learn the cause of the problem - a nail had pierced a neutral supply cable in the loft space, and amazingly, the house in qustion was built in 1992 ! Point to note - just because wiring has been in place for some time, don't assume it can't be at fault... God bless Bob (Bellway) The Builders.