Water cylinder causing boiler to stay on?

[johny_99]

Hi all

 

I was hoping someone could advise on what might be causing an issue I'm getting with my boiler / hot water cylinder setup.

 

For some reason, turning the thermostat on the hot water cylinder up past 40°c causes the boiler to turn on, and if I leave it above 40°c the boiler turns on/off intermittently. Usually every 10/15 mins the boiler would turn on for 10~ mins and turn off again. If I turn the thermostat down, there's a clicking & whirring noise (coming from the metal box next to the cylinder thermostat) and the boiler turns off, and stays off. Also a clicking noise when I turn the thermostat back up, and then the boiler turns on. We have a nest controlling our how water so it should only turn on for 30 mins in the morning and 30 mins late afternoon.

 

The installer doesn't know what's wrong and insists it's not a fault thermostat. I'm also reluctant to get him back in as I'm not convinced he knew what he was doing as he said it could be a wiring issue but doesn't know.

 

The setup is quite complicated (at least to me as I know nothing about this) as we have a wiring centre with a nest, underflowing heating hub, cylinder thermostat all having cables going into it. I will attach photo's, but I don't know how useful they'll be considering the mess of cables.

 

 I was just wondering if anyone had seen this issue before and had any recommendations?

 

Thanks

[ProDave]

I have never quite got into the Nest things, but to put it simply if someone has connected a Nest to control the times of your hot water heating, they have done it wrong.  The Hot water is working from the cylinder thermostat, so if the cylinder thermostat says the tank is too cold it puts the boiler on.  all perfectly normal in a conventional setup.

 

What are you trying to achieve with the Nest?

[johny_99]

Hi Dave

 

That's interesting. We have the nest controlling our upstairs heating (regular radiators) and our hot water cylinder. The nest is programmed to heat the cylinder for 30 mins twice a day. I had thought this was how it was meant to work as it was the same before the new boiler/tank was installed. I thought the cylinder thermostat was connected to the wiring centre to bypass the nest and turn the boiler off when the water was up to temp.

 

So the cylinder thermostat is meant to keep the water at a constant temperature all day/night? That seems a bit wasteful for us and we would be happy just heating the water a couple times a day.

[ProDave]

All I am saying is i am not up to speed with how these nest things are supposed to work.

 

If it was working before and you have had someone fit a new cylinder then he either did not know or did not understand the Nest and has wired it as a conventional system.

 

Normally a hot water cylinder would be controlled by a time switch and the cylinder thermostat.  You need an electrician to re connect it to the Nest.

[PeterW]

That wiring centre has been played with. And it’s not wired correctly for either S Plan or Y Plan as there are links in place going nowhere. 

 

For example, 6 doesn’t look right, and someone has hacked into the live feed somewhere where that red electrical tape is. 
 

I would find a new heating engineer or electrician and then ask them to rewire a new wiring centre correctly for S Plan. 

[johny_99]

16 minutes ago, ProDave said:

All I am saying is i am not up to speed with how these nest things are supposed to work.

 

If it was working before and you have had someone fit a new cylinder then he either did not know or did not understand the Nest and has wired it as a conventional system.

 

Normally a hot water cylinder would be controlled by a time switch and the cylinder thermostat.  You need an electrician to re connect it to the Nest.

 

I believe the nest is working as intended, as in it does turn the boiler on to heat the water at the set times. I believe the nest is supposed to act as the time switch you're referring to?

 

Could it be that the cylinder thermostat doesn't know about the nests set on/off times in the morning/afternoon (wired wrong), and is constantly trying to heat the water if it's not up to temp? That would explain why the boiler turns on/off all day/night if the cylinder thermostat is turned up. We only have our boiler set to 60°c, perhaps that's not high enough to heat the cylinder being set above 40°c?

 

5 minutes ago, PeterW said:

That wiring centre has been played with. And it’s not wired correctly for either S Plan or Y Plan as there are links in place going nowhere. 

 

For example, 6 doesn’t look right, and someone has hacked into the live feed somewhere where that red electrical tape is. 
 

I would find a new heating engineer or electrician and then ask them to rewire a new wiring centre correctly for S Plan. 

 

Hi Peter

 

Thanks for that. I had expected as much as the installer really didn't seem that competent.

 

Don't suppose you or anyone here knows of a decent guy in the Staffordshire area?

[ProDave]

It sounds like the cylinder stat is in parallel with the nest not in series with it.

[Gav_P]

I would get someone in to look at that wiring centre as PeterW says. It’s definitely less than ideal. 
 

I also second what prodave says about it being wired in parallel instead of in series. 
 

looks like it should be an quick easy fix tho... assuming the hive and stat are both wired into that wiring centre. 

[johny_99]

Thanks all! will get someone in to look at rewiring it.  

[SteamyTea]

15 hours ago, johny_99 said:

The nest is programmed to heat the cylinder for 30 mins twice a day

What happens if the cylinder is not up to the desired temperature after 30 minutes, does it totally isolate from the rest of the system.

 

And was the system working correctly before the Nest was fitted?

Edited November 9, 2020 by SteamyTea