Changing Potterton EP3001 to a new Nest Thermostat

[Original_Pug]

Hi all,

New here but been lurking for a while; you've helped with many a DIY task to date so I'm indebted already!

I recently bought a Nest Thermostat for our quite old but fully working boiler (Potterton Profile 60e). It is controlled via a Potterton EP3001 controller, and feeding into that is a Drayton Digistat scr wireless thermostat receiver.

I wanted to replace the EP3001 (an sd also replace the Drayton) as my hot water can only come on with the central heating, not individually).

I did ask for quotes but noone has come back to me and honestly I think it isn't too difficult (have some Self-taught electrical experience).

If I swap the Drayton for the nest it will be very simple, but not what I want (unless you tell me.otherwise).

So I looked at the EP3001 wiring and hope it's a case of swapping the N L 1-5 etc wiring from the Potterton to the nest. Is it as simple as that?

Only complication is the ep3001 backplate has more wiring options that the nest.

Potterton has A B C D in front of the N L 1 - 5

Nest has N L 1 - 5

Drayton Has N L 1-4

There are also a lot more wires to the left and right on the EP3001 backplate (I think these are multiple N and earth's which would needc in a junction box before coming out into the nest? If so to where in the nest?) Or is that a bad assumption?

Questions are:

Is it as easy as swapping the like for like between the ep3001 and nest by copying the wiring labels?

What are the A, B, C & D for? Maybe the wireless controller which will not be used?

The block of blue wires to the left and green/yellow to the right - what do I do with these?

I think I have an s-plan system, as I have two honeywell inline valves (picture will explain), does that affect anything if I'm just copying the wiring?

Pics should be attached,a showing wiring inof the controller backplate, the general layout of my system a (2 x valves circled), the valves mentioned above and the wiring diagram on the rear of the EP3001.

Thanks again for all help!

 

[muggles]

Ah, you have one of the more interesting (read complicated) installs! The old EP3001 is a combined programmer and wiring centre. You essentially need to completely rewire your system from scratch - take everything out of the EP3001, transfer it all to a wiring centre (except the cables for the SCR) then link your Nest in to that. About an hour's work for someone fully familiar with central heating wiring, but somewhat difficult to train someone to do via an Internet forum.

 

[stem]

The EP terminals are printed on the back of it as per your photo

So it's a matter of moving the wires from the EP terminals to the Nest Heat link terminals that have exactly the same function.

So:
wires in EP N ..... Nest N

wires in EP L ..... Nest L (for now discard the link to EP5 we’ll come back to the links later) Once the link has gone, the remaining wires in EP5 will need to be moved to Nest L.

wire in EP 3 Hot water on.....Nest 6 Hot water call for heat

wire in EP 4 Central Heating on... Nest 3 Heating call for heat

Then add links so that Nest terminals L, 2 and 5 are electrically connected together.

EP Terminals A B C & D don't have any function as far as the programmer is concerned, they are just terminals to facilitate the wiring. So you will need 4 new terminals for them so that all of the wires in A remain connected together, as will all of the wires in B, C & D

The same applies to all of the neutrals and the earths on the far left and right. Normally I sink a new backbox in the wall behind and locate all of the new terminals in there.

You will also find it hard to get several wires in the Nest terminals, so for example in the case of the L terminal, I would also connect all of the wires into a new terminal and the just run one Live to the Heat link.

Please do not underestimate the complexity of this task. You need to be extremely electrically competent to do this and fully understand how your heating system works. If you inadvertently transpose wires or mix them up it will be almost impossible to resolve over a forum. So please don't proceed unless you know exactly what you are doing.

Finally you will have to be decommission the existing room thermostat. It can't just be disconnected, the two thermostat live switching wires at will need to be 'bridged' ie connected together to complete the circuit. As a temporary measure it can be set to its maximum setting, but it's not really a permanent solution.

Edit
Or you could do what @muggles suggests. He posted whilst I was typing.

 

[Original_Pug]

Thanks Stem (and muggles), really appreciate the time you've spent in responding.

Between posting this earlier and now, i wired the nest in, in place of the Drayton controller (super easy as it was only N L 1 & 3 with the earth) into the EP. I had to link L & 2 but it turns heating on and off as I need it perfectly.

Honestly I may leave it like this - water needs to come on the same everyday all year so not sure having water on the nest will be worth it anyway?

With your answer above if I change my mind I know how to (your instructions make sense). I'd label every wire, but you're right the nest box is terrible to wire into.

The thermostat is totally wireless, so I'd say it could just be binned as the nest replaces it, no?

Thanks again

 

[stem]

If the Nest Heat link is wired in as a direct replacement for the room thermostat, instead of the EP then yes, you can just 'bin' the old stat.

The Central heating at the EP should be set to be permanently on 24/7 otherwise it could interfere with the operation of the Nest.

 

[Original_Pug]

If the Nest is a direct replacement for the room thermostat, instead of the EP then yes you can 'bin it'.

Yep, that's how I currently have it. I removed the wires from the scr box and wired them into the heat link, which is connected to the EP as was the scr.

Now as long as the heating is "constantly on" on the EP, the changing the temp on the nest switches the boiler on/off, and the scr thermostat and receiver are totally out of the loop (in a draw actually).

Originally I wanted it to control hot water too, but on reflection honestlyi have that heat an hour in the morning and an hour at night everyday, which I can set with the EP.

 

[stem]

as my hot water can only come on with the central heating, not individually

I'm guessing that you didn't resolve that. [unless the EP is faulty] The EP is designed to provide independent control of water and heating so it should have been doing so. If you find now that even with the EP heating set to be permanently 'on' that the hot water still doesn't work independently from the heating, the fault will be elsewhere.

If it was the other way around ie the heating would not come on without the hot water also being on then it's possible the EP has been set to 'gravity mode' of operation.

In this case, I suspect that there is a fault with your hot water's motorised valve. The motorised valve is wired to the EP & Cylinder thermostat, and when heat is required by both they open the valve. Inside the motorised valve is a small switch that in turn starts the boiler & pump when the valve is fully open. My guess is that the hot water controls [EP & thermostat] open the valve OK, but the switch doesn't operate so the boiler doesn't start up. Then when the heating valve opens, the switch inside that starts the boiler & pump so both the heating and hot water can work.

 

[Original_Pug]

Hhhhm the issue is actually that the controller doesn't allow me to set a time for HW or/and CH.

It has an on&off time for the morning, and an on/off time for the evening for each day.

You them have auto, cont, once options for HW & CH - so they come on together by the programmer, and the CH was triggered by the Drayton (but it was crap)

 

[stem]

Ah OK, so you could have the hot water on 'cont' and the heating on 'auto' and the hot water would still work on its own when the heating was off in the period between the two auto times. In which case the Nest will have resolved it. I thought that you meant that the hot water didn't physically work at all unless the heating was actually running at the same time.

 

[Original_Pug]

Ah OK, so you could have the hot water on 'cont' and the heating on 'auto' and the hot water would still work on its own when the heating was off in the period between the two auto times. In which case the Nest will have resolved it. I thought that you meant that the hot water didn't physically work at all unless the heating was actually running at the same time.

You've got it! Well the opposite of it actually, but similar.

My EP has CH set to constant and the nest switches the boiler on/off based on its settings .

HW is set to auto and runs via the program in the EP, for a couple of hours at different times of the day.

All in I avoided a bigger job and it works as we need it!

Only question really is there was an earth wire in the scr wiring which wouldn't connect to Nest, so I capped it. Should be ok?

 

[stem]

Only question really is there was an earth wire in the scr wiring which wouldn't connect to Nest, so I capped it. Should be ok?

Eh????.......

The instructions do state that the earth is only required if T1 & T2 are being used to power the Thermostat, but personally I would still park the earth wire in there even if I wasn't.

 

[Original_Pug]

Exactly I wasn't sure if it was better to leave it out or use that, but as I wasn't using T1 & T2 I decided not to bother...

I can go back and do that tho