Nest/Boiler issues

[Mpw7826]

Hey,

reaching out on here as I’m a bit lost in regard to diagnosing the issues I’m seeing and I’m no electrician.
We had nest installed, 2 thermostats of which one does heat and one does heat/water. The heatlinks are wired up to the tank junction box (new build so fairly new system) and we have an ideal logic h15 boiler with a weather compensator.
If we trigger the heating/water via the app/thermostat we hear the heat link click and actuators turn on/off so everything seems to work as expected. However, it seems as though the boiler is constantly ON so it never goes to 00 because the hot water off wire isn’t doing anything which is leading to the boiler overheating and then fault coding. I’ve taken a look at the heatlinks and the satisfied heat and water are not hooked up, but I’m told this is normal? I’m also told the cylinder thermostat should handle the hot water off signal and the nest just controls the valves?
Any help greatly appreciated. The tank is an SPlan dual zone I believe.

Thanks

 

[ianmcd]

hermostat should handle the hot water off signal

you dont use HW off on an S plan only a Y plan system

 

[Mpw7826]

The wiring book for the tank says S-plan but I’m told by Ideal boilers that the boiler is
not getting a 240 volt from cyclinder satisfied or domestic hot water off.
This is for the weather compensator so removing it may fix the issue?

 

[ianmcd]

The wiring book for the tank says S-plan but I’m told by Ideal boilers that the boiler is
not getting a 240 volt from cyclinder satisfied or domestic hot water off.
This is for the weather compensator so removing it may fix the issue?

Again DHW off and DHW satisfied are only wired in on Y Plan, not on S plan, weather compensation or not

 

[Mpw7826]

So I’m a bit lost, the weather compensator didn’t seem to make any difference, the boiler is still intermittently faulting FA which means reverse flow but the hot water is working (it’s heating the tank).

 

[Deleted member 267285]

Take a photo of your cylinder layout including the motorised valve(s), as you said it’s as you believe?

 

[Mpw7826]

 

[Mpw7826]

Water valve is on left behind and 2 zones at front. Hope that helps.

 

[flameport]

S plan.
HW off / CH off are not required, which is why they are not connected to anything.

 

[Mpw7826]

I turned it off at the mains and then back on and it sat on 00 for a while and then turned on before faulting with FA (hot water and ch off on nest). So at the moment we can get CH and HW and I can hear the valves turn on but the boiler never goes into standby when there is no demand.

 

[ianmcd]

sunds like you have a sticking end switch on one of your zone valves

 

[Mpw7826]

I checked that, the voltage on the orange accurators wires when everything off was dead. If it was stuck I’d expect some voltage?

I’m looking at the diagrams for wiring for the boiler and then with the weather comp for S plan. It looks like if it has weather comp then it has HW OFF hooked up on the cylinder stat and then to SL2 on the boiler, maybe this isn’t hooked up correctly if the HL isn’t providing HW off?. In theory if I remove weather comp and SL2 it should work as expected?

 

[ericmark]

Neither of those plans makes sense, you will not have a seprate timer with Nest gen 3 as the timer is part of Nest gen 3,

You had it installed, so why are you trying to fix some one else's error? I did look on how to install Nest with zone valves, and I can't see how it can be done using opentherm, as far as I can see only option is a simple off/on switching,

The boiler may have a run on to cool down, so pump may be powered from boiler or powered with boiler, but getting boiler run on with zone valves is not easy, and I have not a clue how it is done, likely it is not done, best option is likely a by-pass valve which allows water to circulate but not through radiators or DHW heat exchanger.

So in the main all orange wires go together from all three valves so if any valve powered open the boiler and pump runs, when a valve opens the bleed leave goes slack, and often there is a indicator as well. So all valves closed and boiler should be off.

The Y plan and some C plans use the DHW satisfied wire, clearly not a Y Plan as not a three port valve, it seems unlikely it is a modified C Plan, but if it is then that may explain why you need the satisfied wire, but with three motorised valves it seems unlikely a C Plan would be used.

However even if boiler demand is sent the boiler should not go into fault, the by-pass valve should open and the boiler should just cycle on/off.

You don't say what boiler type, don't know is oil, gas, or other, or if modulating or simple off/on. But it would seem more than simple wiring fault, maybe by-pass not fitted? Last house has a gas modulating boiler and by-pass built into boiler, also there was an external by-pass, seems guys fitting it did not realise one built in, no harm anyway, but if the plumber thought by-pass built in and it was not, then this could cause a problem.

However without knowing exactly how wired, it is just a guess, Nest is weather compensated so can't see why there would be a second, I have Nest Gen3 in this house and in theroy the TRV should follow Nest, but have to admit does not really work.

However unless like this house where I have a flat built under the house, which uses same boiler, but independent controlled, can't see the point in central heating zone valves, I have 9 programmable TRV heads so every room independently controlled, dinning room 4 pm to 9 pm. And bedroom off during the day, but craft room next door to bedroom turns to eco once a day, and press button when I use the room to go to comfort.

The zone valve is on/off, I don't want off I want reduced temperature when room not in use, not off, zone valves are a bit useless, not fit for the use as few people will want same times for all up stairs and all down stairs, and can't use ebus control with zone valves so they just mess the system up.

So who ever fits Nest has to decide how far to go trying to make a silk purse out of a shows ear, best would be rip out zone valves and fit Evohome so every room independent, but clearly that's expensive, so some near enough system is fitted instead, which can work don't get me wrong, but the installer has to decide how to make it work.

He should leave a wiring diagram in an ideal world, but clearly that's not the case here, so likely best option is to get him back, and find out what he has done.

 

[Mpw7826]

It’s an Ideal Logic Heat 15 gas boiler connected to a 2 zone S-plan wired tank. It’s a new build so was installed by builders and then we had a nest pro install the nest.
The nest is turning on/off the valves as I can hear them. The old danfoss thermostats that were connected had the HW OFF wired in when I cross reference the diagrams for the tank/danfoss/old photo. The boiler wiring suggests it only needs SL1 connected and this should get triggered by any of the three orange valve wires that are connected. The boiler also has weather compensator attached and SL2 wired, the wiring diagram the comp suggests that the SL2 comes from the HW OFF so is solely for the weather comp. So my thinking is since the nest doesn’t have the HW OFF connected, I either need that connecting or I remove the weather comp and SL2 in which the boiler should then work solely on SL1. Does this make sense?

 

[Mpw7826]

Just to add

“So in the main all orange wires go together from all three valves so if any valve powered open the boiler and pump runs, when a valve opens the bleed leave goes slack, and often there is a indicator as well. So all valves closed and boiler should be off.”

All oranges are together and when one activates the valve turns on and the little lever becomes floppy as you say.
Ideal tell me it fires when it should be off because the HW OFF isn’t connected which should be live when no HW so neither SL1 or SL2 are live.