NEST No Heating, Water Working

[twodoctors]

Hi all,

My old Drayton MT721R somehow broke, so we decided on upgrading to a NEST. I have looked at this forum posts, and have followed all the advice here. I got the hot water to work, but the heating doesn't seemed to be.

So I have a Baxi 100/2HE Plus boiler, which has been working fine.



Forgive me I'm not a plumber. Not sure if this is a S or Y plan... I have the valve and a pump as per picture.



The wiring is going to drive the plumbers out there crazy (probably). Here is what I worked out:



Old Honeywell thermostat now removed. I have noted the wiring before removal:



1 and 3 connected. 2 just floating in the air.



I wired the NEST as described in various posts here:



N and L
L to Nest 2 and 5
CH to Nest 3
HW to Nest 6

Turned heating up to 32C (ambient is 29C at the moment) but boiler is not firing up. In fact the power light is off.

The boiler will power up on "manual boost" so something is working, but there was no heating with that. Water is scorching hot so pretty sure hot water is working (immersion tank heat is wired separately.

I must have wired something wrong somewhere. Please point me to the right direction! Thanks.

Adrian

 

[ianmcd]

in your last pic the orange and grey wires are not connected to anything, they should be the grey wire should be permanent live and the orange wire connects to the same terminal as the orange wire on the HW zone valve, that is the wire that brings the boiler on

 

[twodoctors]

in your last pic the orange and grey wires are not connected to anything, they should be the grey wire should be permanent live and the orange wire connects to the same terminal as the orange wire on the HW zone valve, that is the wire that brings the boiler on

Thanks Ian.

We lived in this house for 10 years and with the old thermostat everything was working fine. The orange and grey wire had been like that all this time. Are you saying the Heat Link needs to be moved up to the junction box and get everything rewired? Any idea of cost involved, including a proper junction box!?

Adrian

 

[ianmcd]

you must have another zone valve somewhere, you have an S plan if those two wires have never been connected, it has never been wired properly

 

[twodoctors]

you must have another zone valve somewhere, you have an S plan if those two wires have never been connected, it has never been wired properly

I certainly can't "take credit" for the wiring. Built in 1980. Is this "standard" back then? Would have got it sorted (now that I know) but for the cost of doing it...

So the hot water is definitely working. I have no idea where the other valves are. Where should I look (but does it make any difference)? I have connected everything from the old system except for the thermostat Lead 2 /neutral (blue) which is now going nowhere.

I shall check the thermostat Lead 1 and 3 again and make sure the snap connector thing is working...

 

[ianmcd]

Dont assume that blue wires in a central heating system are neutrals colours mean nothing in a heating system

 

[twodoctors]

Just popped up to check again.

You are right. The system is wired incorrectly. There is heating works only if hot water is also on. It's a Y system, and incorrectly installed. Just checked. The radiator was on when I turn on the hot water boost to get the boiler going.

I can attempt to wiring it all up in a proper junction box. I can move the Heat Link next to the junction box. How would I wire the grey and orange from the 3 port valve to the Nest?

The previous owner was a (fairly well known local) dodgy builder (we didn't know at the time!), but he bought the house from new. I won't be surprised if the wiring was his work though!

 

[twodoctors]

I think this is me.

orange and grey not connected. I need to connect grey to HW off (Nest 4)?

What does orange do?

This is probably the clearest chart I have come across so far.

 

[ianmcd]

No you are wrong that is a two port valve, you have an S plan, but if it was a cowboy install you might only have one valve, you should have two or sometimes more

 

[ianmcd]

This is a 3 port or Y plan valve

 

[twodoctors]

So this is me then.

So when the heating is switched on by Nest, signal goes from Port 5 to the CH valve. However because I don't have the cable from CH valve to Port 10 --> SL (switch live?) Boiler, it doesn't come on.

However if the water is also on, then there is hot water flow anyway so the CH works.

Is that correct?

So I need to locate HW valve and find the "orange wire" or "Position 10" wire. This should lead to the boiler SL port. Linking the orange wire from the CH valve to this should make the two system working independently?

Where is it likely to be? I have a water tank in the loft and cylinder in the airing cupboard where the junction box is...

Also notice in the photo of my valve, there is some "dodgy wiring" underneath the valve cable. I am going to guess someone botched it to make it a bit longer.

The grey wire likely to be redundant?

 

[ianmcd]

By the sound of things, what they have done is wired it so the HW is always on and the zone valve was getting power to open when they wanted CH, you would never have been able to get heating without HW, hence why the end switch wires are not connected, this can be achieved with the nest but you have to set it to gravity HW even though you dont have that, very uneconomical would be best to get someone in to do it properly

 

[twodoctors]

Took a bit of time to digest that.

So what you are saying is my system is not quite an S plan. It's rigged so that the HW On is wired directly to Boiler SL, that's why there is no HW wiring at all in the junction box. I have no HW Valve. When HW is on the whole system comes on, but CH valve is closed so the there is no CH. For CH to be on, HW must also be on to i) activate to boiler, ii) open the CH valve. Is that correct?

I guess why would you want CH if you don't need HW? Is this typical of older setup? Or did someone cut corners somewhere?

The solution is to add a HW valve and rewire the Boiler SL so HW and CH can switch it on separately? What is the cost going to be like? And is the energy saving, in terms of heating bill, worth the few hundred pounds it will probably cost? Wait till the boiler eventually packs up and get a combi boiler or whatever is the latest?

Hmmmm.

Thanks for taking the time to answer Ian.