Heating Wiring Problem - cylinder thermostat not working

[westward10]

No apologies needed but the forum does have a moral code when it comes to step by step advice. Before you employ another person be sure they understand your situation so you are not wasting further expense.

 

[dfreitag]

Hi again

Before we wrap things up completely, I'd love to have your last opinions on what's going on - I hope that's ok.

Also, just noticed another symptom. One of my radiators (the one right above the boiler) is heating up when I get the hot water to heat..

Your wiring should now resemble the s-plan diagram in the nest instructions minus the boiler being called for and not power cycled.

That's really great! Good to know we reached this

The voltage should only be present on the orange core when the valve is open, the small valves only have a normally open contact the bigger valves also have a white core. Something is amiss there.

B/w orange & brown core I still get

when HW&heat OFF > 244V

when HW&heat ON > 0V

I'm sill not quite sure if this is ok - can someone please clarify?

(PS my Zone valves are 2x Danfoss 087N6609 - link to their website here)

The boiler should only run when there is a connection between 3 and 4. If there's nothing connected in-between the boiler shouldn't run. That PCB looked suspect with all of the flux, I couldn't tell if the joints were dry or take a guess at the function of the repaired section from the photo however.

Do I understand correctly - are you saying this was NOT a new PCB? (the guy who installed it claimed it was and charged accordingly..)

Hopefully you have enough information to get someone to complete the troubleshooting. Good luck with it.

Thanks for all your help @Aaron b - much much appreciated!!

---------------------------------

See below latest photo from wiring box

 

[Avo Mk8]

Do I understand correctly - are you saying this was NOT a new PCB? (the guy who installed it claimed it was and charged accordingly..)

Just to chip in to Aaron b's observations:
I think all one can say is that there is evidence of hand repair to a circuit board that was originally reflowed.
In your photo (post 63), midway along the bottom, between the black plug on the two green/yellow earth wires, and the two blue capacitors, you can see four components that have been hand soldered (the joints are convex shiny blobs rather than the concave reflowed original appearance), and there is flux on the board that in a manufacturing environment would have been cleaned off. There's possibly further rework hidden by the connector.
Boards do get reworked sometimes in the factory, but I would expect a better standard, and the flux to be cleaned.
So it seems clear there has been a repair, but by whom and when we cannot say.

 

[davesparks]

Also, just noticed another symptom. One of my radiators (the one right above the boiler) is heating up when I get the hot water to heat..

Is that radiator in a bathroom? It's normal for the radiatot/towel rail in a bathroom to be connected so that it gets hot when either heating or hot water is on. The theory behind this is to allow wet towels to be dried all year round.

B/w orange & brown core I still get

when HW&heat OFF > 244V

when HW&heat ON > 0V

Are you saying you measured that voltage between the brown and orange of the valve?
If that is the case then you would expect to see 0V between them when the zone is on because both wires should be live at that point. But you might also see 0V between them if something is wrong causing both wires to be dead.

When measuring voltage you are measuring the difference between two points and not an absolute value. So if you measure the voltage between two points which are both live at 230V your measurement will be the difference between them, 230V - 230V = 0V

As for a voltage between orange and brown when the zone is off, theoretically there wouldn't be any, but as you have two floating points and a multimeter you might get any reading between 0V and full mains voltage.

 

[brianmoooore]

Is that radiator in a bathroom? It's normal for the radiatot/towel rail in a bathroom to be connected so that it gets hot when either heating or hot water is on. The theory behind this is to allow wet towels to be dried all year round.

This is a common way of connecting bathroom radiators, but the same effect can occur if a common plumbing mistake is made. If a boiler has a single hot water return port, the return from the HW cylinder must tee into the return trunk nearer to the boiler than any radiator. If not, a venturi effect will occur with the cylinder return water flowing past the radiator tee, sucking water from the radiator branch, through the radiator, along the heating feed trunk from another radiator, and from the return trunk where that radiator tees in. This water will be drawn the wrong way along the return trunk, from the cylinder return, so will be hot, and will heat the radiators.

 

[Aaron b]

If this was something I was asked to look at I would check the voltage on the control to the boiler (call for heating), I would prove the function of the boiler using a link between 3 and 4 I would prove be wanting to prove it was off when the link wasn't in place and that it fired up with the link. If not I'd call valiant and speak to there technical dept.

To prove the nest stat I would want to see the valves move. I think you can press the button on the controller to get it to call for heat. The arm moves on the side and I think it goes loose when energised.

To check the connections through the valves I would probe between earth and the orange from the valve in the energised and the de-energised positions. I'd only expect voltage on the orange core when the valve is open.

 

[westward10]

Thread closed. @dfreitag this has been going on for a week with multiple step by step posts which cannot go on. Find a competent heating engineer.

 

[dfreitag]

OK, so after finally finding a competent heating engineer, I though it could be helpful to share the solution!

Thanks @westward10 for temporarily reopening the thread!

Turns out the culprit was the Heating valve, which was faulty and sending a permanent live to the boiler, independently in which position it was on..

By replacing that valve, the issue was solved. (annoyingly a previous contractor had changed the HW valve - so the wrong one)

(Seems quite plausible in hindsight to be honest, but I guess it almost always is afterwards..)

The engineer also re-did the wiring from scratch, and with a rather clean result - please see below photos of all items.


Hope it is of help for someone out there! I'm definitely relieved to have a working HW and heating systems, before winter and those massive bills hit...

All the best
tsomek

 

[littlespark]

Glad its all sorted....

How did this thread have over 2000 views in the space of a month?

 

[Stu435]

Nest wiring: The green/yellow appears to have been used for 'hot water on', since it's connected to 10 at the wiring box. Wires can be used for purposes other than that indicated by their colour if a short identifying sleeve is fitted over the wire at each end, BUT this does not apply to a green/yellow wire. This can only be used for earth and for no other purpose.
The cable used appears to be only 4 core, so should be replaced by 5 core, with the green/yellow used for the earth connection to the nest, and the grey (with brown sleeves at each end) used for 'hot water on'.

Hi. I know this is a couple of years old but I think just as valid now as then. Does this rule apply for extra-low voltage control wires?