Nest / Hot water issue

[Andy Byford]

Hi all,

I've been having an eternally long nightmare, of which I have only just realised stems from a nest install from back in 2019.

As it turns out, my electricity bill woes are due to my unvented cylinder using its built in (3kw!!) emergency heater, rather than calling for heat from the boiler! So for 2 and a half years, all of my hot water has been heated from this electric backup (Yes, my electricity bill has been stupidly high and I have been going crazy trying to figure out why! I had never thought of this as I thought the hot water was working fine from our gas boiler!)

I have since had a qualified nest technician come out to replace a faulty heat link around a year ago, but I still have the issue.

Does anyone have a clue why my nest / boiler / cylinder aren't working together? My HW schedule in my nest is set to 24/7. The cylinder just isn't calling for heat from my boiler for some reason.

I thought my stupidity maybe mis-wired something, but surely the qualified engineer that came to replace my faulty unit would have spotted an error??

So does anyone have any suggestions for my circa £5000 mistake?

Thanks in advance

 

[ianmcd]

Need more information, pics are best, post pics of the cylinder and assosciated valves thermostats etc

 

[Andy Byford]

There is a ton of info in this post I made back then:

NEST Installation

Hi all, first post here! Please move if it's in the wrong section. I'm quite into my DIY and have been upgrading parts of the house, I bought a Nest thermostat last week and just wanted to check everything checks out, if anyone could give any advice on the below it would be greatly...

www.diynot.com

It has pictures of all the old / new wiring and also the cylinder etc...

Thanks

 

[ianmcd]

When you call for the HW Cylinder to heat, does the DHW Zone valve open ?

 

[Razor900]

If it's been running on the immersion make sure the high temperature cut out on the cylinder thermostat hasn't operated. That would kill the Nests ability to call for hot water

 

[Andy Byford]

When you call for the HW Cylinder to heat, does the DHW Zone valve open ?

It doesn't seem to do anything, the cylinder just uses the immersion heater straight away, the nest app shows that hot water is currently ON.

If it's been running on the immersion make sure the high temperature cut out on the cylinder thermostat hasn't operated. That would kill the Nests ability to call for hot water

How can I check that this hasn't operated?

 

[opps]

I didn't think that the nest would be able to flick the fused spur and turn on the back up heating element.

That said, I have only encountered Nest/Hive set ups on combi boilers.

 

[Razor900]

It doesn't seem to do anything, the cylinder just uses the immersion heater straight away, the nest app shows that hot water is currently ON.



How can I check that this hasn't operated?

Look at the cylinder thermostat there will be a reset button on it. Probably under a screw cap - not the one on the immersion itself though...

If all else fails post a picture on here or look it up in your user instructions. It's probably labelled 'high energy cut out' or similar

If it's tripped it will stop the boiler heating the water

 

[Andy Byford]

Look at the cylinder thermostat there will be a reset button on it. Probably under a screw cap - not the one on the immersion itself though...

If all else fails post a picture on here or look it up in your user instructions. It's probably labelled 'high energy cut out' or similar

If it's tripped it will stop the boiler heating the water

There's a small black plastic cap with a plastic pin underneath it that is sticking out, does that seem normal?

 

[opps]

There's a small black plastic cap with a plastic pin underneath it that is sticking out, does that seem normal?

With the greatest of respect, why don't you post the relevant photos rather than expecting people to trawl through your old posts?

 

[CBW]

I didn't think that the nest would be able to flick the fused spur and turn on the back up heating element.

That said, I have only encountered Nest/Hive set ups on combi boilers.

I think Razor is saying that the immersion could be on, thus preventing the Nest from operating

 

[Andy Byford]

With the greatest of respect, why don't you post the relevant photos rather than expecting people to trawl through your old posts?

I linked the thread so all of the information I used is available, not just the photos. There could be an issue with the original install and that thread is the best way to explain what has happened to get me to where I am right now.

 

[Andy Byford]

To clarify the thermostat type I have attached pictures of it and the valves that are both the same and set to auto.

Our immersion heater switch was on, as even with it turned off the boiler still is not heating the water

 

[opps]

I linked the thread so all of the information I used is available, not just the photos. There could be an issue with the original install and that thread is the best way to explain what has happened to get me to where I am right now.

Sorry, I wasn't being combative. I couldn't be bothered to follow the hyper-link and I suspect that the people most able to help you haven't either.

Old posts often have lots of responses, some of which are not relevant. Busy people don't particularly want to have to trawl through those. I am not intentionally criticising you, but I genuinely think that consolidating the relevant info in this thread is likely to be beneficial.

Best of luck.

 

[Andy Byford]

Look at the cylinder thermostat there will be a reset button on it. Probably under a screw cap - not the one on the immersion itself though...

If all else fails post a picture on here or look it up in your user instructions. It's probably labelled 'high energy cut out' or similar

If it's tripped it will stop the boiler heating the water

I think you might just be a genius. I switch my immersion spur off and pressed this reset switch and (whilst only early days) it seems to have kicked the boiler on for the water! Will see how it goes and let you all know if this fixed it.

Side note, if this little reset button has cost me a ton of electricity for 2 years I'm gonna be annoyed with myself