Replacing Danfoss FP715SI with Nest Third Generation

[ericmark]

This

seems to be the CH (top) and DHW (bottom) links. I don't know why DHW can be turned on/off with a combi boiler, and you have not linked to the manual. I would only connect Nest to the CH and would leave DHW always on.

Seem to remember two DHW options, Eco on and Eco off, with Eco off the boiler had a small reservoir of hot water, so taps don't need to be full on to get hot water, but if used with a shower it can run out and go cold under the shower while the boiler get to temperature.

As said, my home has 14 heated areas, and the TRV heads do most of the control, so a system which will not allow TRV heads to be linked in is rather useless. I have moved to Wiser.

 

[DIYron26]

Thanks @ericmark . That makes sense now after watching some other videos/ reading other threads. One thing that hasn’t been clear anywhere and I can’t find the answer to is if the low/ no voltage “On/Off thermostat input” should remain connected. I assume it should be as the link on the CH that is currently there will do the same job as the nest (for the purposes of the boilers understanding).

Boiler manual - https://www.worcester-bosch.co.uk/support/literature/download/release/6720883858/45568

Thanks again.

 

[ericmark]

Sorry, can't remember what I had worked out.

It would seem Worcester Bosch do not use ISO labels but USA names, I am sure what is calls low voltage should be labelled extra low voltage. So you will not be touching that block of terminals, they are not what in the UK what we call low voltage, we call them extra low voltage.

This

shows the low voltage (50 - 1000 volt AC in this case 230 volt) connections, so it seems this

is the 230V Out L being linked to LR radiator and water, so the LR radiator L and N will go to the thermostat, and that link removed, but since all ready using a thermostat I would have expected the link to have already been removed?

 

[DIYron26]

@ericmark there is currently no thermostat on this boiler, it is in a different property, so I am adding the Nest.

I understand the links etc on the CH/ DHW (LR’s). However on the other side, the ultra low voltage side, there is currently a wire in the “On/Off thermostat input”

. My question is, if I add a thermostat, should this remain in place or be removed? There is no guidance anywhere I can see on this.

 

[ericmark]

I would remove the link L to rad sign, and if boiler stops running, then that's the correct one to switch.

 

[DIYron26]

Update: I have now wired the next in, link is connecting to thermostat and everything appears to be correct, however boiler is not firing when I call for heat on the thermostat. I tried leaving the “On/Off thermostat input” link in place and then without after restarting from the power supply. Same issue.

I did read online that it can take 30 mins+ for the boiler to initiate before it will respond to calls for heat. I didn’t have time today to try this. Does this sound right? Nothing was displayed on the boiler as if it would be “initialising” or as such. Please see wiring of nest

 

[CountryFan]

Can you post a photo of the front of the boiler?

 

[DIYron26]

@CountryFan only photo I have atm

 

[CountryFan]

Ok, can you confirm that it’s on for heating at the boiler, eg not in summer mode and temperature set high enough at the boiler and Nest?

 

[Johnmdc]

You need to plug that light blue plug back in that you have removed. Apart from that the nest looks to be wired correctly.