Advice wiring a thermostat please!

[xena]

Hi there

I would really appreciate help with this.

The thermostat for the downstairs heating in our house has never worked, so I took a look at it today. There are 3 wires going to it: green/yellow, blue and brown.

The thermostat is a Drayton RTS1, which has 4 terminals: Neutral, Live, 3 (Call for heat) and Earth.

Currently, the wiring goes: Brown to Live, Blue to Neutral, and Green/Yellow to Earth.

This leaves nothing going to the 3 (Call for heat), which I guess is why the thermostat isn't working!

I'm guessing that one of the following is the case:

1) the green/yellow wire may actually be the 3 (Call for heat) 2) the green/yellow is actually neutral, and the blue is the 3 (call for heat) but I need to know how to check this without fusing the system! Also this would leave no earth - is this likely?

I've got a digi multimeter, and there's 230 Volts coming down the brown (when checked against either the blue or the green/yellow), so that's in right, but how do I find out how to rewire the other two?

Many thanks for any suggestions. xena

[Dave Plowman (News)]

Using an earth as a 'live' is all too common a bodge where plumbers get involved in wiring. And some DIY types too, who should know better.

You've got a couple of options.

Do the job properly, and replace the cable with a Triple and Earth. The earth is probably not needed, but you do need three properly insulated and identified wires for this type of stat to operate correctly.

Wire the stat without the accelerator coil. Then you'll only need two wires. But it won't be as accurate.

Replace the stat with a programmable one. These are battery operated and only need two wires. They'll soon save their cost in reduced fuel bills.

Either way, it looks like you'll have to delve inside the connections at the boiler end to sort out this bodged wiring.

[Set Square]

Does that mean that the heating doesn't work either - or has the stat been by-passed in some way?

Sounds pretty likely!

The type of stat which you have *needs* 4 wires, and can't safely be installed with 3. A common short-cut employed by some plumbers is to use the green/yellow wire for the switched live (which you refer to as the "call to heat"). This is unsafe for two reasons. Firstly the stat needs to be eathed, but isn't when this is done. Secondly, a wire which any reasonable person would expect to be earthed is, in fact, live!

If you want to do this properly, you have 3 choices:

1) replace the 3-core cable with 4-core 2) run a seperate 4th wire from the stat to whatever it connects to (possibly a junction box in the airing cupboard) 3) replace the stat with one which needs less wires. For example, modern electronic programmable stats only need *two* wires - since they don't need to be earthed and they don't have a built in accelerator heater needing a neutral return.

In order to find out exactly how yours is wired, you need to find the other end of the cable, and see what each of the cores is connected to. If you can identify the type of system you have in terms of one of the "plans" shown in

you can look at your stat connections with reference to the appropriate wiring diagram.

[Dave Plowman (News)]

The laugh is that if you used it for the neutral there would be less chance of getting a belt off it.

[xena]

The heating does actually work. As long as the face plate of the thermostat is on, the heating works. If it's taken off, then it doesn't. I don't know why that's the case! The only thing I can think of is that maybe one of the wires is a "satisfied" wire rather than "call to heat" hence why it always thinks the heating should be on?

Um, of all the above options, I prefer number 3! I think the RTS7 works with 2 wires, so maybe I'll get that.

Cheers, I'll have a look at that now.

Many thanks for your help, Set Square :o) I'll post back with how I get on.

[xena]

Um, how significant is the fact that the heating is on?? Does it mean that I need a weird reversed thermostat?!

TBH, the thermostat is plastic cased, and if I sleeve the wires with the correct colours, would this be so bad? After all, the rest of the wiring is likely to be to the same standard and I'm not replacing the lot as the house is for sale!

Is this still an option if, as it looks like, my wiring seems to be "reversed" (i.e. it's constantly on even when the wires aren't connected, or is this normal?

I've looked upstairs, and our heating/plumbing system is a nightmare! We have two circuits, one for the downstairs heating, and one for the upstairs. There are wires everywhere, and nothing is labelled. The only thing I found which might be of any use is "EARTH = N" written on the plasterboard behind the connection to the upstairs thermostat.

Cheers xena

[xena]

Hi Dave Thanks for your reply.

This isn't an option, I'm afraid. It would mean too much disturbance and the house is currently up for sale! Besides, I'm not smart enough to do it and I can't afford to pay anyone else to do it.

Not sure what this is to be honest - is this the neutral connection?

Don't mind doing this - please see my other post for more info.

Very grateful thanks :o)

[L Reid]

Green/Yellow

I recently installed one of these on to my heating system. I'll see if I can find the instructions for the thermostat if that's any use to you?

L Reid

[L Reid]

The RTS 1 is double insulated and does not need earthed.

L Reid

[TW]

The RTS1 is an electronic stat and requires a neutral to work. I'm not sure whether the relay is actually normally closed so if the neutral is not there, it never switches off.

Are you sure that the blue is in the neutral and not the switched live terminal?

It's possible that if the blue wire is in the neutral terminal, and it is really the switched live that the stat is in series with the pump but I would expect the resistance of the stat electronics to be too high for that to work.

What wires are in what terminal numbers?

No, the fact that the heating stops when the stat is removed from the backplate means that the wire is call for heat.

I'm pretty sure the RTS1 is double insulated so you "could" do this, It's bad practice though.

Drayton Digistat does not need a neutral (it has a battery) and will fit on the same backplate.

[L Reid]

Green/Yellow

Ok, in addition to the green/yellow, is there a separate earth? Alternatively, is the green / yellow fully sleeved, or is it the earth of twin & earth (i.e. a bare wire with a yellow sleeve over a small part of it)? Also, do you know what model of programmer/timer that you have? It may be that you might have to take the casing off of that to confirm the wiring.

[Set Square]

Fair enough, if you have a manual, and it *says* that. But the OP did say that it had an earth terminal.

My old Danfos stat (which I've now replaced) sounds fairly similar from the description, and had a notice inside saying "This device MUST be earthed" or somesuch.

[L Reid]

I think the earth terminal is provided to give you something to attach any previous earth wire if changing from a metal cased unit to this one (so you don't have a bare wire you don't know what to do with in the case). It does definately say that the RTS1 is double insulated on the instructions.

[L Reid]

I've had a look over my copy of the instructions, and there's an "important note" which reads:

"RTS thermostats are ELECTRONIC with a relay output. Unless connected to a

230V mains supply, the relay will not operate, no 'click' will be heard and the call for heat contact will remain open"

Can you hear the thermostat 'click' when you turn it?

[xena]

Blue is definitely in neutral. There is nowt in the switched live.

There is only one numbered terminal, that 3 (call for heat). There's nothing in there.

Yes the instructions say that it is double insulated.

[xena]

Yes, as long as the heating is turned on, it does click.

[xena]

I have the instructions, just having difficulty understanding them!!

Cheers

[xena]

No, there is no separate earth.

The cable is bog standard 3-core flex, not twin and earth, so fully sleeved.

The programmer is a Horstmann Channel Plus H37.

Thoughts at the moment are that the brown wire is in the right place (live). The green/yellow is the neutral The blue is the switched live (call for heat)

Does anyone know of any multimeter checks I can do to verify this?

And thank you everyone *so* much for your help!! It's the first time I've posted on here, and the response has been amazing :o)

Thanks you all xena

[xena]

I've found a PDF of the RTS1 here with a diagram that shows that it is normally open.

[Owain]

"xena" wrote | No, there is no separate earth. | The cable is bog standard 3-core flex, not twin and earth, so fully sleeved.

This fails electrical safety standards on one, if not two, counts.

(1) Flex should not be used for fixed wiring. For some reason it often is by people who call themselves Heating Engineers but whom I wouldn't trust to wire up a rabbit snare.

(2) Whether or not the thermostat is double-insulated, all circuit cables must have an earth (circuit protective conductor) running within or parallel to them and an earth must be present at all accessory points.

As the house is up for sale it is possible that this would be flagged by a surveyor and your overall electrical installation queried.

Possibly the best course of action would be to find the other end of this flex (hopefully a 'wiring centre' near the boiler, in the airing cupboard, etc), remove the flex and replace with a wireless thermostat.

Owain