topic Re: Heating only comes on when hot water is on in Nest Thermostats

Heating only comes on when hot water is on

Newlands — Mon, 13 Nov 2023 12:52:59 GMT

We have a oil fired central heating system. The heating will only turn on if the hot water is on. If the hot water is not on, the central heating pump will turn on, but the boiler will not fire up. This means that controlling a target temperature is not possible unless the the hot water is turned on 24/7. Is there a way of making this work better, or even to turn the hot water on and off automatically when the heating turns on and off in response to the temperature falling below a set number?

Re: Heating only comes on when hot water is on

Frustratedddd — Sun, 12 Nov 2023 15:10:08 GMT

I assume you are in the UK?

Would this be a new install?

Re: Heating only comes on when hot water is on

Newlands — Sun, 12 Nov 2023 15:31:52 GMT

Yes UK. It was installed approx 1 year ago. It has been like this since installation.

Re: Heating only comes on when hot water is on

Frustratedddd — Sun, 12 Nov 2023 15:47:49 GMT

The simple answer is, wiring incorrect!

Who installed the thermostat?

Would the boiler be an old one?

You should be able to do the following if you have a 3rd Gen stat, and an Oil boiler, wired correctly.

1. Heating On - The boiler will fire up, and the pump will run until the stat temp is reached, the boiler will then cut out and the pump stop. The cycle will start again when stat calls for heat.

2. Hot Water On - Boiler will fire up but no pump running

Can you upload a picture of the Heat Link connections?

Re: Heating only comes on when hot water is on

LarisaL — Mon, 13 Nov 2023 12:29:12 GMT

Hi there, thanks for reaching out! This might be happening because of various reasons and in situations like this we perform a click test to determine if the issue is related to your thermostat or to another part of your heating system like a valve, wires or with the boiler itself. That being said, please go near your Heat Link and turn the heating on from the app and let me know if you hear a click. You should hear a click when you turn on the heating and another click when you turn it off. Just to make sure that the relay is working properly, please try that 5 or 6 times and let me know if you hear a click at every command.

Re: Heating only comes on when hot water is on

Frustratedddd — Mon, 13 Nov 2023 12:39:39 GMT

A Click Test?

The user says the this has been working for a year, which means at least one relay is working!

That means that the click test passes! The trouble is, how does the user deteremine which relay is not working, or in fact both are working?

Would you not think that if the issue has been there since the fitting, perhaps an incorrect install?

Re: Heating only comes on when hot water is on

Newlands — Mon, 13 Nov 2023 12:57:22 GMT

Yes, the relay clicks and the pump starts up, but the boiler does not fire up. I just reread my original post and realised I missed out an imprtant "not"! The sentence should read "If the hot water is not on, the central heating pump starts up but the boiler does not fire up"

Re: Heating only comes on when hot water is on

Frustratedddd — Mon, 13 Nov 2023 16:20:39 GMT

Basically what you are saying is this!!..........

You should be able to do the following if you have a 3rd Gen stat, and an Oil boiler, wired correctly.

1. Heating On - The boiler will fire up, and the pump will run until the stat temp is reached, the boiler will then cut out and the pump stop. The cycle will start again when stat calls for heat.

2. Hot Water On - Boiler will fire up but no pump running

......but - ONLY if wired correctly!

The important part is this line from the user...

It was installed approx 1 year ago. It has been like this since installation.

Are you correct? ''the relay clicks and the pump starts up, but the boiler does not fire up'' Where does the heat come from if the boiler does not fire up and the thermostat is calling for heat? Would that not mean, if calling for heat the boiler has to fire up?

After seeing so many Oil boilers with Nest stats incorrectly wired at the Heat Link, I question the wiring more than the relays as it's an original problem.

Many installers wire terminals 2&3 for the pump, and 5&6 for the boiler, but on an oil boiler sometimes not the case. This is the reason I asked for a picture of the Heat link connections.

Re: Heating only comes on when hot water is on

LarisaL — Mon, 13 Nov 2023 16:04:46 GMT

In this case, I recommend you call an installer since the Heat Link seems to be working as expected, because you can hear the clicks. The installer should check the wiring of the Heat Link to make sure it was done as in our installation guide and also check other parts of your heating system.

Re: Heating only comes on when hot water is on

Frustratedddd — Mon, 13 Nov 2023 16:16:31 GMT

I would agree, and there is a but!

The Google installation guide does NOT show an Oil boiler of an age which this user might have. The oil boiler could be an old one which uses just the burner and a circulating pump no valves etc., which means none of the installtion guides would be of use to them.

This goes back to my request at the start to ask for a picture of the Heat Link connections.

Don't you just love an easy thermostat install?

A reply from the user is now required to go any further.

Re: Heating only comes on when hot water is on

Frustratedddd — Mon, 13 Nov 2023 16:18:24 GMT

Can you confirm if this is an old boiler with just burner and pump?

Re: Heating only comes on when hot water is on

Newlands — Mon, 13 Nov 2023 17:47:19 GMT

Yes that is the case. Does this mean that the current functionality is all that we are going to get?

Re: Heating only comes on when hot water is on

Frustratedddd — Mon, 13 Nov 2023 18:26:38 GMT

I take it your boiler is an old one, and just has a simple Burner and pump, no valves nothing else, correct?

Should the answer be yes, then your wiring is wrong!

Wired correctly, and you should get….

1. Just heating required - the pump and burner will run, and when temperature reached both will cut out. The pump will run on its own if temperature has not been reached, and the boiler stat will cut the burner out when that’s reached. The pump will keep running for brill desired temperature, and the burner will kick in and out depending on the boiler stat setting.

2. Water only - no heat to rads as Nest set to your required setting.

Still need a picture of the Heat Link connections to give me an idea.

Who installed the Nest?

Re: Heating only comes on when hot water is on

Newlands — Mon, 13 Nov 2023 18:49:17 GMT

Thanks. The answer is yes. No valves. Nest was installed by an electrician. I don't know how to expose the connwctions for a picture.

Re: Heating only comes on when hot water is on

Frustratedddd — Tue, 14 Nov 2023 13:33:58 GMT

Yes you have a standard old Oil boiler and people just can’t work them out! Any good electrician should be able to install, as they are so simple.

I guess without looking the pumps connected to the heating relay, and the burner to the water relay. Half right, but will never work if the relay isn’t configured correctly.
I think they have connected a standard simple configuration just to get it working. I’ve seen dozens of these wired wrong. Best get them back to correct it so your system works as it should.

The wiring is under the Heat Link cover, just loosen the screw at the very bottom and lift the cover off. Very simple.

This screw here

Re: Heating only comes on when hot water is on

AlexD — Thu, 16 Nov 2023 09:44:23 GMT

Hi, I wanted to check in. Did you manage to have someone look at the wiring? Keep us posted on how things go.

Re: Heating only comes on when hot water is on

Newlands — Thu, 16 Nov 2023 17:14:14 GMT

Thanks for your help. It's very much appreciated. I have someone coming to look at the wiring in a couple of weeks. I will let you know what happens.

Re: Heating only comes on when hot water is on

Frustratedddd — Thu, 16 Nov 2023 17:51:29 GMT

You are very welcome.

Yes please update me when the job has been completed, but could you take a photo of the Heat link connection when the cover first gets removed as it is now. Also, can you take a picture of the Heat link connections when the wiring is completed.

Just curious how connected now, and what you end up with.

Final result should be able to do this if connected correctly.

1. Just heating required - the pump and burner will run, and when temperature reached both will cut out. The pump will run on its own if temperature has not been reached, and the boiler stat will cut the burner out when that’s reached. The pump will keep running until desired temperature, and the burner will kick in and out depending on the boiler stat setting.

2. Water only - no heat to rads as Nest set to your required setting. JUST the burner will fire up, NO pump.

Re: Heating only comes on when hot water is on

LarisaL — Fri, 17 Nov 2023 10:47:19 GMT

Hi there! I'll leave you here the installation guide so you can check the wiring diagram, if you need them. We'll be waiting for your update. Keep us posted.

Re: Heating only comes on when hot water is on

Frustratedddd — Fri, 17 Nov 2023 13:02:36 GMT

@LarisaL Could you please show me in the Installation Guide exactly where it shows any connection of an oil boiler this user has?

They do not have a Y plan, or S plan or a Combi boiler, the only help the guide gives is the Heat Link terminations. The installer who wires up the system, if they are unaware of this boiler type it will not work correctly.

The connections are very straight forward and simple, but very few installers ever get this system correct. I think this clearly is the issue with the users installation at present, after one years use they have had enough.

The user states they have an electrician coming in a couple of weeks, and I have asked for pictures to confirm the finished connections. I am very interested to see the end result.

Please DO NOT lock this thread it's not over yet - Thank you