NEST Installation on Oil Heating System - Danfloss MK42 9ER

[btolsta]

Good morning everyone,

I know there is many a thread on this sort of thing but the issue i am having is a strange one so i wanted to double check what I have done. I replaced my danfloss programmer with a nest about 6 months ago. It works as expected so programs, call for heat and water all work perfectly. It does fire tho for 3 minutes twice every hour without us calling for anything. The boiler is in the kitchen and the megaflo is in the airing cupboard so i know its not frost protection kicking in. It has made me want to double check my wiring before i look at the zone valve.

Please find below the original wiring and what i have wired in.

Thanks in advance to anyone who can give it a once over

 

[stem]

You have swapped them over so that the wiring is 'like for like' in that what you have now with the Nest, replicates what you had before. I can't really say more than that without knowing what's connected to the other end of each of the wires. However, what you have done to swap them over, is exactly what I would have done.

I can't determine which position the switches are set to on the original programmer though, but I can't see how that would cause the symptoms you describe. Most of them relate to the programmer functions so are irrelevant in this instance, the only one that could have an effect is the 'pumped / gravity' switch but from your reference to the Megaflow and the wiring photos, I would expect that you have two port motorised valves that control the heating and hot water and so it would have been set to 'pumped' which is what the Nest needs. [A gravity system with a Nest is a bit complicated]

If the heating and hot water is set to 'off' and the boiler fires up, does the heating / hot water actually come on?

Sometimes there is a frost stat elsewhere, such as an outbuilding where a boiler is located, that may be operation.

 

[btolsta]

You have swapped them over so that the wiring is 'like for like' in that what you have now with the Nest, replicates what you had before. I can't really say more than that without knowing what's connected to the other end of each of the wires. However, what you have done to swap them over, is exactly what I would have done.

I can't determine which position the switches are set to on the original programmer though, but I can't see how that would cause the symptoms you describe. Most of them relate to the programmer functions so are irrelevant in this instance, the only one that could have an effect is the 'pumped / gravity' switch but from your reference to the Megaflow and the wiring photos, I would expect that you have two port motorised valves that control the heating and hot water and so it would have been set to 'pumped' which is what the Nest needs. [A gravity system with a Nest is a bit complicated]

If the heating and hot water is set to 'off' and the boiler fires up, does the heating / hot water actually come on?

Sometimes there is a frost stat elsewhere, such as an outbuilding where a boiler is located, that may be operation.

Hi Stem,

Thanks for the sanity check. I was pretty sure the wiring was the right way as the system but its great to have a second opinion. In answer to your question the heating and water dont come on when the boiler decides to wake itself up. Just runs for about those three minutes twice an hour and then shuts off. I never hear the pump kick into life. Its almost like its just keeping its storage warm. I checked the boiler manual which is for my Camray 5 that i have and it says:

1:5.9 FROST PROTECTION If there is any danger that your Boiler may freeze up during severe weather conditions, it is recommended that you consult your installer who will be able to advise you on an appropriate course of action, either by installing a frost thermostat or the addition of system anti-freeze

So it looks like it doesnt have a frost stat by default in it and i havent seen one anywhere. I have included a picture of the boiler. I have no idea what that contol stat phail does on the right hand side of the picture but it does have the word stat in it Its just sort of hanging in the boiler cavity. I have also included pictures of the megaflo valves. They are always at auto and seem to be working.

 

[Hairymelon]

Dumb question. But on the nest is the live link in 2 or 3. I can’t tell

 

[btolsta]

Dumb question. But on the nest is the live link in 2 or 3. I can’t tell

It’s in 2, and then the loop from 2 to 5.

 

[Hairymelon]

It sounds like a wiring fault is calling the boiler on permanently and it runs without pump or valves on till boiler stat cuts in. However you would think the overheat stat would operate

 

[btolsta]

It sounds like a wiring fault is calling the boiler on permanently and it runs without pump or valves on till boiler stat cuts in. However you would think the overheat stat would operate

Actually.....we are having an issue with lockouts that looks thermal as if we leave the boiler door open we don’t get them. So any ideas what the wiring issue could be as I thought it was good

 

[Hairymelon]

Do you mean burner lockout or overheat reset ?

 

[btolsta]

Do you mean burner lockout or overheat reset ?

It’s the burner lockout since you mention it not the overheat. The reset kicks it into life straight away with no need to bleed it so it doesn’t look like air. Filters have been replaced.

 

[Hairymelon]

Cam5 or cam 3 ? Balanced flue ? (This is a different fault most likely ) not related to mystery fire up. Possible flue gas recirculating.


Check if boiler being called on 240v when nest off

 

[btolsta]

Cam5 or cam 3 ? Balanced flue ? (This is a different fault most likely ) not related to mystery fire up. Possible flue gas recirculating.


Check if boiler being called on 240v when nest off

It’s a cam 5 with a balanced flu as far as I know.

So when you say switch the nest off do you mean the heatlink controller that’s mounted on the wall?

 

[Hairymelon]

So that ch and hw are off Check there is no power to call boiler on. If there is and pump is not running there is a wiring fault if the pump is running it’s most likely the danfoss zone valve needs replacing.

 

[btolsta]

So that ch and hw are off Check there is no power to call boiler on. If there is and pump is not running there is a wiring fault if the pump is running it’s most likely the danfoss zone valve needs replacing.

Thanks very much for the suggestion. I will give that a try hopefully tomorrow and post my results.

 

[oilboffin]

Check pump pressure.Bob

 

[btolsta]

Cam5 or cam 3 ? Balanced flue ? (This is a different fault most likely ) not related to mystery fire up. Possible flue gas recirculating.


Check if boiler being called on 240v when nest off

I took your advice but sods law could not find my multimeter yesterday so i just went old school with it. I pulled out the CH heat wire from the nest and left it hanging for two hours while i watched the football in the kitchen (good excuse . The boiler never fired once. Screwed it back in and now the boiler isn't calling for heat randomly. My best guess is that it was somehow touching the live wire beside it and completing the circuit and therefore calling for heat all the time. Going to leave it for a couple of days but fingers crossed that's it. I have also ordered a new motor capacitor as i think that is what is causing my random lockouts. The future is looking brighter Thanks to all that took the time to look and reply.