4 siemens 3 port valves burnt out in a year.

[RayPlumb]

Changed a clients burnt out 3 port siemens DVA3 heating valve head like for like this time last year. Just put it down to normal wear.
Then it burnt out in April. I thought unlucky, siemens not great but ok and changed it. Told client to make sure not to cover it etc as I know they can get hot some times.
Checked all working as it should. Then end of November it burnt out again!!. Told client to get electrician in to check wiring, which he said he did but not sure what he checked. Said it was fine so reluctantly another valve head went in as still under original years warrantee. Checked workings ok. Now yesterday he called to say valve burnt out again. 4 in a year?? Cant be the valves surely..
It is always first thing in the morning when the programmer calls for hot water. They can smell burnt plastic smell.
I have said after the last one I wanted to changer to honeywell but meant drain down etc.
Any Ideas what is doing this as I'm reluctant to put another valve in until I find the cause?
Thanks

 

[Gasmk1]

The head isn’t leaking is it, when cold the leak could get onto the electric and short it out ?

 

[RayPlumb]

The head isn’t leaking is it, when cold the leak could get onto the electric and short it out ?

Never noticed anything. The first valve I changed I thought there was a water stain and on the cover and quizzed about the cupboard being used to dry clothes as the valve is about 2 feet above the floor standing boiler in a tall narrow cupboard. But was assured it wasn't used for wet clothes??.
The valve is fitted on its side...I will check tomorrow as it will be pretty cold.

 

[ShaunCorbs]

Find there not the best for lasting but normally get 3 years out of them

 

[John.g]

Maybe voltage check?.

 

[Ben-gee]

Is valve stiff so motor is struggling and burns out?
Either way I’d be looking at changing whole valve, and like you say- to something decent.

 

[RayPlumb]

Is valve stiff so motor is struggling and burns out?
Either way I’d be looking at changing whole valve, and like you say- to something decent.

Hard to say if stiff. Does move only about 30deg.

 

[RayPlumb]

Maybe voltage check?.

With power off and fuse out .Check all connections and all wiring in the right place. Disconnected old siemens valve . Although checking continuity on the wires picked up 38ohms on Live to neutral looks like it is coming from the boiler (grant)?? Phoned the electrician and he said it should be fine. Is it.???
I have then fitted the new Honeywell and done the various voltage checks 240 volts etc Htg and Hwater on valve in mid position, Got 240v Orange and white and 67volts back feed on grey..

 

[RayPlumb]

Could a poor circulation cause a burn out. drained system twice as little dirty. Also pump was set at 2 for a bungalow , although pretty old system.. When I tried the old one for movement without the head there was a thud (not heard before) when I moved it manually across to either hot water or heating not sure which.? Could pump be too high? With the new honeywell valve there was no thud. But still worried about ball getting stuck pressure/ vacuum holding it in place and burning out valve? Would turning down pump help?

 

[John.g]

If it's not thudding (with motor attached) then I wouldn't be too worried, I have seen posts on here where reducing the pump speed/head has cured the problem, if it's a newly installed pump then except that it's a 8M pump, it shouldn't cause problems on speed2. I don't see any pump pressure capable of holding the valve in place as its a geared motor and will provide a high torque.
One reason given for relatively short (but not as short as yours) mid position valve lives is that it will hold its last known position so if CH only was selected on nightly shutdown then the motor will stay "running" in its normal stalled condition overnight, if HW selected then there is no power to the valve. If a spare HW programmed time is available then maybe no harm to time this for as short a period as possible after the CH is finished at night, the valve will then stay un powered.