honeywell valve fault?

[keniff]

hi guys heres one for yah! went to a call out yesterday as boiler had shut down all timer clocks etc had lost power, so starting from the mcb i started to trace the loss of power, i was stumped i had live feeds going everywhere! then i found i was getting 240v between neutral-earth from all points boiler and controller! any way after finding this i decided to go to the main wiring centre of the heating disconnected all neautrals and found it was the neutral from the hot water motorised valve that was giving 240v any ideas what could have happened to the valve? any one had this before? and i have checked return neutral and ch valve is working fine!

 

[lamb]

Any disconnected neutral will give 240v when there is a load on and the line is still connected.
I would suggest there is a fault with the return neutral, either open circuit or high resistance not allowing current through.
Turn off the fused spur, isolate the consumer unit and lock off, pull the circuit concerned line from the MCB and place in the associated neutral bar, then measure r1+rn at the fused spur.
If this reading is fine, with the power still off, measure neutral resistance accross the switch of the fused spur.
I personally have had this problem twice, once was a broken neutral between the c/unit and fused spur, once was a dirty switch neutral contact not allowing current through to a water heater.

 

[keniff]

the neutral return seemed to be fine, the other valve (seperate for central heating) is working fine now the hot water valve is disconected, the boiler jumped back to life and now heating controllers are working, got R1+RN continuity from spur back aswell. this is what i find strange?! the hw valve used the same neutral path as all that is still connected and now working! its a hard one to explain.... but im just waiting on new valve hoping this helps?

 

[lamb]

I agree that does sound strange.
Still, at least with S-plans you can hook each valve open manually so the system can still work while you wait for parts.

 

[keniff]

yep im confused.com! thanks for your help though!

 

[nickblake]

it could be a syncron motor fault if its a three port valve they are very complex
The three port valve is a masterpiece of clever engineering, in that it manages to move to one of three positions using only a cheap non-reversible AC motor, a spring, a couple of micro-switches, a resistor and a diode, and act as a relay for the boiler into the bargain! However, it has obviously required quite a bit of lateral thinking to conjure up, and its operation is thus not easy to understand. Here's how it works.
The spring pulls the valve to position A, while the motor winds it towards position B. If the motor is left continuously powered, it will stall in position B, but if it is fed with DC (produced with the resistor and the diode), then it will stall in any position. Two micro-switches, operating just either side of the 'A+B' point, are used to define this position.
This is the circuit diagram of the innards of the valve:

 

[keniff]

just a update on this, changed the valve all works fine so not sure what was wrong with the valve!

 

[ringer]

I take it you mean you changed the actuator head, not the valve. Did you take the old one home and wire it up to see if the fault still occurred?