Replacing Altech ALTHC001 Controller with Nest 3rd Gen

[agwright99]

Hi

I'm trying to replace my Altech ALTHC001 controller (which I understand is basically a SALUS EP200) with the Nest 3rd Gen controller.

We have a Worcester Greenstar 30CDi System Boiler. As far as I can tell it's a closed gravity fed system with a hot water tank. The showers are on a separate pump from the hot tank which turns on on demand.

The Altech has Live and Neutral connected, as are the Hot Water OFF, Hot Water ON, and CH ON. The CH OFF does not seem to be connected in the current config. (See attached pic)

My current guess is the wiring needs to be (Altech/Nest):

N=N
L=L
HW OFF = 4(?) Hot water satisfied, or 5? (HW Common)
HW ON = 6 Call for heat
CH ON = 3 Call for heat

Would this work? All of the Nest diagrams also include a connection to another of the CH terminals so I'm a bit concerned need to re-wire to the boiler which is probably outside my skillset.

Any help much appreciated.

 

[ianmcd]

No that is wrong

CH ON = 3 on nest
HW ON =6 on nest
HW off = 4 on nest
And a link between L-2 &5
N=N
L=L

Any existing room thermostats will need to be linked out

 

[agwright99]

No that is wrong

CH ON = 3 on nest
HW ON =6 on nest
HW off = 4 on nest
And a link between L-2 &5
N=N
L=L

Any existing room thermostats will need to be linked out

thank you very much for this. I think I’ve done it correctly (see pic) but can’t seem to get the boiler to fire with the nest (though all powered etc). How do I “link out” the existing thermostat? Short the existing connections? I feel like this might be the issue.

 

[ianmcd]

Short the existing connections?

Yes you will have to link out the old thermostat, post a pic of the wiring in there

 

[agwright99]

Yes you will have to link out the old thermostat, post a pic of the wiring in there

Thanks - looks like the attached - guess I just join red and yellow for now?

 

[ianmcd]

Yes to test it quickly just put both wires into the same terminal,

 

[agwright99]

Yes to test it quickly just put both wires into the same terminal,

Cheers - will do. Just reverted it all to the old system for tonight so we’ve got heating etc & will try again tomorrow

 

[agwright99]

Had a bit of a 'mare with this - reverted everything last night but same issue - even with the old controller and thermostat reconnected the boiler won't fire for hot water or heating on command.

Everything seems to be powered fine - the boiler is on and operates from the boiler panel, the controller and room thermostat have power, the valve has power (it switched when I put it on manual). I've not check the pump - don't know where it is (could be integrated with boiler?)

I haven't touched wiring behind the room thermostat. I believe this is fine.

I have reverted the controller wiring (before and after pic attached - I note an earth wire is loose in the picture - subsequently fixed). This seems ok.

I have opened the circuit/wiring box to check - I hadn't touched this till today. (Pic attached for reference).

There is some wiring behind the controller which includes a loose connection (third picture attached). This might be the issue as I could have knocked it. The grey wire from the boiler I guess is a live return(?) and connects to the red control wire which I think goes to the valve(?) via the circuit box. The yellow seems deliberately blanked off and appears blanked in the circuit box (top right). The light blue looks like it might have been attached to something behind the controller. In the circuit box I think this joins another light blue in junction 2 - which seems to connect to a dark blue wire from the valve and a black wire from another cable (which seems to be a mains type cable).

I can't figure out if this was supposed to be connected to the controller, the live return(?) or is a red herring. In my "before" photo it didn't really show so I'm stuck to be honest!

Any help greatly appreciated before I call out an engineer...

 

[ianmcd]

You shouldnt have went anywhere near the wiring centre, the nest simply replaces the Altech, and the existing room thermostat is linked out, put everything back the way it was in the wiring centre, then replace the Altech eith the nest , join the wires in the room stat, then post pics of what the wiring looks like now, colours of wires mean nothing in heating system

 

[agwright99]

You shouldnt have went anywhere near the wiring centre, the nest simply replaces the Altech, and the existing room thermostat is linked out, put everything back the way it was in the wiring centre, then replace the Altech eith the nest , join the wires in the room stat, then post pics of what the wiring looks like now, colours of wires mean nothing in heating system

Thank you so much for your patience with this!

I didn’t touch any wires in the wiring centre - was just trying to figure out if my issue was this loose wire behind the controller. I think it actually goes to the thermostat cos the blue wire there is also blanked off. So perhaps that’s not the issue.

I’ve reconnected the nest as per picture, (will tidy up when it’s working) and joined the wires in the room thermostat (second picture). Boiler is alive (as before, third picture) but still not actually heating any water, despite the nest being on manual.

I feel like I must have blown the valve or something as surely the boiler would still heat the hot water regardless of the central heating. annoying!

 

[ianmcd]

your wiring all looks correct , you need to pressurise your boiler but that isnt your problem, on the left hand side of the control panel on the boiler, the bottom button with a pic of a chimney, press that and hold that and tell me if the boiler fires up

 

[agwright99]

your wiring all looks correct , you need to pressurise your boiler but that isnt your problem, on the left hand side of the control panel on the boiler, the bottom button with a pic of a chimney, press that and hold that and tell me if the boiler fires up

Just finished the kids bath (plenty of hot water) and came downstairs - boiler is on and firing - so I guess hot water must be working somehow... pic attached - could be it’s just keeping the tank warm?

I flicked the valve over to manual and the rads are heating up for now.

does that help give a clue what might be wrong? Still got the controller set to “all on” for now.

 

[ianmcd]

I dont think the problem is with your nest, I think you have done something at the other end, google nest 3rd gen with Y plan and that is how yours should be wired

 

[agwright99]

I dont think the problem is with your nest, I think you have done something at the other end, google nest 3rd gen with Y plan and that is how yours should be wired

I blew the 3A fuse yesterday on the initial install - nothing seemed to be damaged but I wonder if it did break the valve - is there any way to test the valve (or could it be a pump or something?)

thank you for all your help so far - might be less serious than I feared at least

 

[ianmcd]

no the 3 amp fuse is there to protect everything but sometimes relay and micro switch contacts fuse together before the protection fuse blows , I am going to tag another user on here @stem , I respect his views and he may have spotted something that I have missed