Nest and Danfoss System

[MacLad]

Apologies for another Nest question.

I`ve finished installing the Nest Heatlink to replace a Danfoss CP715. The rest of the system seems to be all Danfoss too (three way valve, tank thermostat on a Y type system).

Installed without any major issue - central heating working fine but don`t seem to be able to use the hot water boost or schedule hot water.

The heatlink is in the kitchen under the boiler and I can hear a click from possibly the heatlink when I call for hot water on the thermostat. Three way valve and boiler are upstairs in the airing cupboard.

I`ve attached the wiring diagrams for the installation. The brown wire (3 to 6) I had assumed that this was a switch. Is this the issue or is it another live?

I have the old thermostat to remove in the hall way but I`ve maxed out the temp and central heating working without any issue.

Any help greatly appreciated.

 

[CBW]

I’m guessing it did work before the nest changeover? Have you gone to the 3 port and checked it?

 

[MacLad]

Yes. Everything worked well before. No issue with the 3 port.

I`ve not touched any wiring in the heating wiring centre - only replaced the CP715 for the Nest Heatlink.

 

[CBW]

Take photo of wiring just to confirm, diagram is good, on second one, is there a link between heating on and hot water on? The green line?

 

[MacLad]

The second diagram is the wiring centre with the different inputs. I`ve ran the cables from the back box behind the Nest using wago wire connectors so colours changed slightly but wiring diagram still accurate.

The bottom two wires on the centre I think are to the old thermostat (which is cranked up high at the mo and which I plan to remove) and then move the bottom black/ brown sleeve wire into the white/ brown cable on the valve. As I said CH seems to be working no problem. Only issue is I can`t use hot water boost and the boiler doesn`t appear to fire when the schedule kicks in.

Pictures attached.

 

[CBW]

If it’s only happened with the changeover, it’s either pure bad luck that the 3 port has failed or a wiring issue. When I’ve checked the wiring for hot water call which is orange in the wiring centre, so that one is going to be needed at hot water call at nest, which must have been mixed up.

 

[MacLad]

I’ll take another look tomorrow and check the wiring. Maybe also try the Danfoss controller back in to test the 3 way.

 

[stem]

central heating working fine but don`t seem to be able to use the hot water boost or schedule hot water.

You have wires in the correct Heat link terminals, so provided that they are securely connected, and all you have done is move them over to the Heat link as per your diagram, and it was working before then it all looks to be as it should do. It's worth checking the connections to 4, 5 & 6 for security they look OK, but Heat link terminals can be a bit fiddly.

With Nest, whilst you have control of the central heating temperature via the thermostat / app, it doesn't control the hot water temperature, that is still done by the hot water cylinder thermostat. Sometimes when this symptom has been reported, it's simply because the cylinder is full of hot water already, so regardless of the Nest status, the hot water won't come on until it cools and the cylinder thermostat switches it on.

When you switch the hot water on using the schedule, or boost. Does the Hot water light on the Heat link illuminate? If not there's a communication error somewhere.

Also, what happens when you override the Nest using the button in the centre of the Heat link? All of the lights should be on and be green.

If they are, has the hot water come on now? (cylinder thermostat allowing of course). If it does the wiring and valve etc are OK.

 

[MacLad]

Thanks Stem. The wiring does appear to be ok on checking the heat link.

The three green lights are all on when I hit the button on the front of the nest. The hot water schedule activated the boiler tonight although only the steady green light illuminated. Is this normal operation?

Can you also confirm that the black/ brown sleeve wire (in the wiring centre) to the brown/ white wire on the three port valve is from the current room thermostat? I am planning to replace this with the black/ brown sleeve wire from the bottom terminal after verifying this and them removing the cable from the system.

 

[stem]

When you hit the manual button, it will turn on the hot water [drip symbol] and also the heating [wave symbol] If that is what happens and the central heating and hot water [hot water cylinder thermostat permitting of course] come on, then the wiring is OK.

When the schedule is running, the appropriate light / lights should be lit, depending upon what the schedule is set for. So, when the schedule says 'heating on' the heating light should be lit, if the schedule says 'hot water on' the hot water light should be lit.

So the below is wrong if the hot water schedule is set to be on. The 'drip' should be lit. So that suggests to me that there is a scheduling / communication problem somewhere.

The top circular light is just to say the Heat link has power and is working OK.

Can you also confirm that the black/ brown sleeve wire (in the wiring centre) to the brown/ white wire on the three port valve is from the current room thermostat?

I would expect that to be the switched live from the original room thermostat if it's still in circuit.

 

[MacLad]

I’ve still not managed to get time to check the wiring over but the heat link is keeping water hot and also radiators as per schedule/ nest thermostat.

It may be paranoia but radiators seem a little too hot? The boiler is an Ideal HE15 so I’ve turned down the stat on the front to about 1/3 of full scale from just over a half.

 

[stem]

How hot the radiators get when the heating is on has nothing to do with your Nest. The boiler thermostat is responsible for the temperature of the water leaving it. All the Nest is, is a simple on/off switch. It turns the radiators on and off, and that's all it's doing.

If you are worried about it, try turning the boiler thermostat down to its lowest setting for an hour or two and see if the radiators are cooler then, if they are you will know the thermostat is working.