Ghost In The Machine

[WeeStu]

Hi all, I've got a right brain scrambler job on, and it's doin' me nut in.
Called out to check dhw on constant heat.
System is approx 10yrs old and is s plan. The system is run by programmer and has no cylinder or room stats. All bar one rad have trv's fitted. According to customer the system has run perfectly since it's installation.

Over the last couple of weeks the customer has noticed that the boiler is running and heating the hot water even when the programmer has been turned off. I went yesterday and found that the only way to turn off boiler and dhw is at the main electric isolating switch.

The wiring at the programmer is secure and no visible signs of scorching that would indicate a problem there.
The wiring for the zone valves for both the dhw and ch is in good condition, secure and showing no signs of scorching etc.

The wiring in the wiring centre is also secure and showing no sign of shorting.

As mentioned above there is no room stat or cylinder stat on the system, and the wiring centre has been configured to accommodate this.
I checked all the wiring using a multimeter and everything seems to be fine. I also removed the programmer from the wall and switched the electricity back on, and, lo and behold, the boiler fired up and started heating the dhw with the programmer disconnected and in my hand!!!!!!!
The ch is unaffected in any way with this issue.
Any help with this one would be gratefully received as my brain hurts now :-(
Thanks in advance

 

[Whn1]

Wow!? I hate these ones when the customer stresses that it has been working correctly.. Have you checked that it's wired correctly? Could be a p/l going into th s/l of the boiler..

 

[Puddle]

Maybe micro switch on hot water valve stuck on or syncron motor stuck with valve in open position ,power through motorised valve micro switch to boiler does not go through programmer

 

[kay-jay]

i agree with whn1, just because a dopey custard has only just spotted an issue doesn't necessarily mean that it has just started happening.

 

[Whn1]

i agree with whn1, just because a dopey custard has only just spotted an issue doesn't necessarily mean that it has just started happening.

Completely agree!
http://www.ukplumbersforums.co.uk/central-heating-forum/33783-any-advice-guys.html
remember this one? In the end it was just wired incorrectly, he cust will still argue that it was once working correctly..

 

[WeeStu]

Thanks for the quick replies, I believe the wiring in the wiring centre is correct, so it's off to check the synchron motor isn't stuck on. 🙂
Thanks

 

[snowhead]

Domestic Hot Water zone valve needs a new motor, it's failed open.

Check the switched live from the DHW aux Switch at the wiring centre, it'll be live whereas the S/Live from the heating won't be.

.

 

[WeeStu]

thanks Snowhead

 

[buckley plumb]

Maybe micro switch on hot water valve stuck on or syncron motor stuck with valve in open position ,power through motorised valve micro switch to boiler does not go through programmer

i agree mysons the worse for this

ant

 

[stevetheplumber]

just work back from the boiler to see where the live is being fed from my money is on a micro swith stuck closedon the hot water valve as some one has said dont always listen to the customer ive often gone to systems where both valves have failed and the customer is adament that there was no problem before

 

[tamz]

Domestic Hot Water zone valve needs a new motor, it's failed open.

Check the switched live from the DHW aux Switch at the wiring centre, it'll be live whereas the S/Live from the heating won't be.

.

Zone valves don't fail open.
It is the micro switch sticking. Easy fixed.

 

[jtsplumbing]

Why not just re-wire and add cyl stat & room stat ? got to be the way to go for safety of hot water temp and for running costs, overall costs of parts not that high, but will benefit customer !

 

[ManchesterGas]

Zone valves don't fail open.
It is the micro switch sticking. Easy fixed.

I have had a 3 port stuck in the mid position. even with the power off, it still wouldn't return.

 

[WeeStu]

Domestic Hot Water zone valve needs a new motor, it's failed open.

Check the switched live from the DHW aux Switch at the wiring centre, it'll be live whereas the S/Live from the heating won't be.

.

Cyber pint for your advice mate. I didnt think the zone valve could fail open, every day is a school day.
Thanks to all of you for your replies, everything al back to normal now and customer well chuffed. 🙂