NEST gen 3 fitting on Honeywell programmer and room stat

[jimyol]

Thanks TTC, I can confirm that the Nest heatlink is wired directly, the previous programmer has been removed.

 

[jimyol]

Thanks Stem, sensible test which I hadn't thought of. I've tried this and it makes no difference. In your 31 aug 2017 post you suggest - if I read it correctly - that linking the thermostat in this way is not the same as linking the terminals in the main junction, is this correct and worth me trying?

 

[stem]

It doesn't matter where the link is made, electrically speaking the end result is the same. [Heat Link terminal (3) is connected via the wire link wherever it is made, to the motorised valves white wire] Also, if you have reinstated the original thermostat and set it to maximum and it doesn't work, then the thermostat wiring isn't the problem.

The only other things I can suggest are, that you check the wire in terminal (3) 'heating call for heat' and make sure that the screw is firmly connected to the conductor and not the insulation. Heat Links are fiddly even for those used to making electrical connections and I have come across several installations that didn't work because of a bad connection.

I assume also that you have connected the 'live' on Heat Link (L) to terminals (2) and (5) as well.

 

[jimyol]

Thanks Stem, I've re-read your earlier note and studied the wiring in the main junction box, now understand better and happy with the thermostat bypass link. I've checked all my wiring, confirmed all connections tight and in line with requirements, also confirm I've connected the 'live' on Heat Link (L) to terminals (2) and (5) as well.
I've done a factory reset on the heatlink and re-booted the thermostat, gone through the setup process again. Now what is happening is that the heating is working but only when the hot water is timed or boosted to "on". I can live with this for a while if necessary, hoping to change boiler for a combi before too long, but it doesn't seem right. My suspicions are now with the 3-way valve - would you concur, and is it likely to be a wiring issue or mechanical sticking?
Your help really is much appreciated.

 

[stem]

It's possible that the motorised valve is faulty. They have an internal switch that when in heating only mode triggers the boiler. When the hot water is on, the cylinder thermostat triggers the boiler, but if the motorised valve microswitch was faulty, when the hot water cylinder had heated up the heating would go off also.

It also would be coincidental if the motorised valve failed at the exact same time you installed the Nest, I assume it was working OK before?

Do you have a connection from the Heat Link terminal (1) 'Heating satisfied' that goes to the motorised valve's grey wire?

 

[jimyol]

Thanks again Stem. I had assumed that the valve was working OK before but now I'm suspicious. We just moved to this house a few months ago and the heating seemed to be functioning OK, however I did feel that the hot water was too hot so I tuned down the tank thermostat a few weeks ago. Looking back this didn't have any effect and the hot water is still a bit too hot which I guess is consistent with a faulty valve.
There's no heating satisfied connection.
Is the motorised valve microswitch replaceable, or is the solution to replace either the actuator or the complete valve?