Hi all,
I have a remote timer unit on my existing central heating system, a British Gas own brand job, which is goosed, and the timer part is broken. So a friend had a spare unit lying around, a Danfoss TP4000 which he says should be compatible, but he hasn’t got time to fit it at the moment. Iv had a look and there are 4 wires going into the switch from the boiler, and are wired onto ‘N’, ‘L’ and 2 and 4 of the following terminals.

IMG_2811 by john.bernardon, on Flickr

So I need to connect those 4 wires onto the new unit with the following terminals if its at all possible….

IMG_2812 by john.bernardon, on Flickr

I know there must be guys out there that can give me direction. And I know this is purely off the record assistance, just need to get this working ASAP as the baby is now back from hospital and the snow is lying here! Boiler works fine by just using the on off switch part of the current timer, just obviously a pain as we can’t get the house warmed automatically in the morning. Any help much appreciated.

get a sparky!!!

You don’t need a sparkie! I just swapped mine from an old thermostat that needed had four wires, to a new Honeywell C907 (fantastic compared to the old one) that takes two wires.

I did actually get it wrong due to me reading the correct instructions but thinking they said the opposite, thats why they fit fuses to the boiler plug 🙂

P.S It was DIYnot.com forums that will give you a hand.

As far as I can see you don’t need the L and N, probably because the new unit has a battery. Don’t forget to disconnect the L and N at the boiler end though – don’t just leave them flapping around. I would probably put a terminating block on the end of each just to be sure as well.

Then 2 on old unit is same as 2 on new unit

4 on old unit is 3 on new unit.

That should do it. Your risk of course but these are normally just set so a switch closes whenever heat is needed

+1 for that particular Honeywell timer as well. If it is the one I think it is then it learns when to switch the boiler on to get the house up to temp in time and also does a good job of consoling the temp once it is up.

p.s… and of course isolate the whole thing and check it is off with a meter before working on it (never forget that stage). The baby needs a dad more that a boiler :). I thought you had done that already but I see the old unit just pulls off. Disclaimer: I am not an electrician

Looking at what you’ve got you have a 240V supply running a timer and possibly 24v from the boiler to terminal 2 and back to the boiler via terminal 4 to switch it on. The replacement is a 240v switch so probably not compatable. Buy a suitable replacement and get someone to wire for you. If you end up putting 240v down the 24v circuit it’s gonna get a whole lot more expensive for you!

The replacement is a 240v switch so probably not compatable

Wrong

Buy a suitable replacement

wrong – it’s fine

get someone to wire for you

Right 🙂

what YP said above – do not put 240V down the 24V system – could be expensive to fix – should be a quick job for a professional!

I’m pretty sure switch 2 to boiler 2 and switch 3 to boiler 4 is correct.

For reference, on the switch, N/c means normally closed, N/o means normally open, where normally means what it is set to when the switch is off.

I think what the voltage thing means is that if you’re running a purely battery switch, ie. Not switching the boiler live feed, you can use a 24v rated switch – it doesn’t matter anyway, as a switch rated to 240v will switch any lower voltage fine. So by having a 240v switch, you’re okay.

I think possibly In theory you are supposed to get a gas safe person to certify any central heating boiler wiring.

How exactly do you people going on about 24v think that a simple switch is suddenly magically going to take 24v at the input and dump 240v into the output?
I’ve got a 240v switch at home working with a 3.3v circuit board and it doesn’t suddenly explode because it doesn’t like the number written on the back of the switch.

Appears to be bog-standard 240V changeover switching:

Connect 2 to COM
Connect 3 to N/C
Connect 4 to N/O

Your thermostat is designed for 230V operation so you’ll also need to connect the link between L and 2 if not fitted. You don’t need a gas-safe person to verify the change of a thermostat – at least according to the bloke that serviced my boiler.

I think Flaperon may possibly have got the new and old switches mixed up.

Please ask your friend who gave you the switch as there is now a mixture of both correct and incorrect information on this thread and if you knew which was which you wouldn’t have asked the original question. I hope that doesn’t sound rude – I’m just trying to prevent an accident.

leffeboy – ahh… that makes more sense. It never occurred to me that the OP wouldn’t have posted a photo of the connectors inside the boiler and treated us to a portrait of his broken thermostat instead. Feel a bit thick now.

I think Leffeboy is correct but I’m no electrician and I’d want to see where the wires went to be sure. I would guess L & N are only there to power the timer and no longer required in the new timer. Arguments about the device switching 24V are irrelevant.

Is your buildings and contents insurance up to date if it all goes horribly wrong 😯

Hi guys thanks for all the responses. Yes the new switch is battery powered as opposed to the old one which is powered by the mains. It does sound like its not quite as simple as I first thought. 🙁 suppose ill try and get a spark to have a look. Thanks for all the responses guys.

I’d just like to say, I’m not an electrician and I have no idea. Y’know, rather than adding to the fog and that….

It does sound like its not quite as simple as I first thought

😥 It is quite simple really and if you are comfortable with changing a light switch safely you would have managed.

Congratulations on the baby btw – welcome to a life of chaos!

Best left to the ‘Destroy It Yourself’ Muppets on here as usual. No further comment! 🙄

And this is what is lovely about all requests on here (or any forum). There are some people people on here who are correct and some who have it completely wrong. You just can’t tell unless you either know the people or know the answer already. Fortunately the advice in all cases is correct.

A tip I was given, when you work out what two wires are required, isolate the wires and check its dead, then directly connect the two wires with a chocolate block.

Turn everything back on, turn the heating on and the boiler should fire. This could save you from potentially damaging the thermostat if you have got it wrong. Obviously if the hot water tank is calling for hot water then the boiler will fire anyway, so check if the rads get warm.

Once you are happy, electrics back off and wire up the thermostat.

dont get a spark they will not know what to do.. get a part p certified ch engineer who works on them all day. and for all the elf and safety freaks.. you do not need to be gas safe reg to work on your own appliance.. of course that doesnt mean you ll be safe or not kill anyone but you wont be doing anything illegal..

Just to say Leffeboy, I took the plunge and followed your direction and it works a treat! 🙂 Cheers all for the help