Honeywell CM927 Installation question

[jonnyfonny]

Hi everyone,

I have one of these devices myself and I love it. I got mine fitted last year when I was having some electrical work done, and I have since bought my parents one.

Anyway, as my trusted electrician lives so far away I thought I might have a bash at installing it myself. My question is, can I simply leave the heating controls connected to the boiler switched to "constant", and then replace the thermostat (very old looking thing with a horizontal dial - measurements in fahrenheit), with the transmitter unit supplied with the honeywell? The thermostat at the moment is in one of the bedrooms, a long way from the boiler.

Or, will I have to wire it into the boiler? Access to the back of the boiler might be a bit tricky, as it's in a purpose built boiler house outside. It's a worcester-bosch combi I believe from the mid 90's. Not sure on the model number.

Thanks for any help/advice!

 

[staz1000]

Hi Jonny,

I recently fitted a CM927 to my house but it's the only heating job I've done so I'm no expert.

I was replacing a programmer which was battery powered and literally only acted as a switch to turn the boiler on and off. It was essentially a clever roomstat so you should be able to do the same.

The problem I faced though was the relay box for the CM927 needs a permanent live to power the box AND a switched live which turns on the boiler so I had to put a shorting link between those 2 terminals on the back of the relay box.

I did also have to swap some wires over at the boiler end but I can't remember what I did exactly, sorry.

It's definitely possible though and was a pretty easy job if you've done some electrics before.

 

[jonnyfonny]

Thank you for your reply.

I'm hoping to have a look at it this weekend if I get chance.

I really hope that it is just a case of replacing the thermostat in the bedroom with the relay box (with a bit of modified wiring, like you say).

I rang a couple of local electricians but they wanted to charge me £80 for fitting. Only cost me £35 last year. Mind you I did have a few other jobs for him to do at the time.

I'll try to update how I get on. Hopefully I won't leave my parents with a cold house!

 

[D_Hailsham]

The problem I faced though was the relay box for the CM927 needs a permanent live to power the box AND a switched live which turns on the boiler so I had to put a shorting link between those 2 terminals on the back of the relay box.

Be very careful!!!

Some boilers are controlled by switching 230Vac but others use low voltage of volt-free switching. If you insert a link between the L and A terminals and connect the relay box to a boiler which uses low-voltage or volt free switching, you will damage the boiler.

The info will be in the boiler Installation Manual. If you are not sure, post the make and exact model of the boiler.

 

[staz1000]

I had an electrician around doing some work in my garage at the time of me fitting my programmer so I asked him for some advice and he was pretty clueless. I don't expect that they're all like that of course but I'm glad I was able to do it myself, for free, and properly.

 

[jonnyfonny]

Thank you for your replies.

I've just been in touch with my dad and the boiler is a worcester-bosch i-series boiler (the 24i).

Unfortunately he says the last heating engineer he had in disappeared with the boiler manual. So, could one of you more knowledgable ones help me to determine whether it has 230V switching please? I don't want to break the boiler with the cold weather due back any day now!

Oh, and I've just noticed that this boiler is recommended for small houses/flats. They live in a 4 bed detached. Shouldn't they have a more powerfull boiler?

Thanks again!

 

[mikely]

You can get the manual here:
http://www.worcester-bosch.co.uk/in...ure/24i-discontinued-november-2004-literature
It is mains switching. You need to connect the thermostat receiver so that it returns the switched live to the boiler as shown in the manual for which you need a minimum of 3 wires between the boiler and the receiver (L, N, switched L). See Fig 5 and 9 in section 10.

You can leave the existing timer connected and set to constant but it is redundant once you have fitted the CM927 and may confuse operation of the system in the future. Better to link out its terminals at the boiler or timer, remove the timer, putting its wires in a choc block, and just put a cover plate in place of the timer.

On the rating question, combi boilers are sized on DHW flow rate, not so much on heating power. 24kW should be plenty for a 4 bed detached. I only have a 15KW boiler in my 4 bed detached.

 

[jonnyfonny]

That info is very helpful thank you.

I hope to tackle it one morning this week, so be prepared for more questions if I get stuck!

Cheers guys. This forum is awesome!

 

[jonnyfonny]

Ok, I finally got round to fitting this thing over the weekend and it was pretty straightforward (thanks to all the help on here!). I do have a problem with the wireless range though.

I'm going to try and move the relay box right to the top of the boiler house as far away from the boiler as possible. At the moment it is about half way up the inside (still about 1ft away from the metal housing of the boiler). The problem is the thermostat needs to be within about 6ft of the relay box to get a signal.

Could the batteries be an issue? I've used the batteries that came with the thermostat, although they have just been sat in the box for over a year. Would the battery power effect the wireless range?

A bit stumped I'm afraid. I've done the signal test (where the light flashes green on the relay every 6 seconds) but it cuts out even if I move the thermostat 10ft across the kitchen! Ideally I want to place it in the lounge.

Any help greatly appreciated!

 

[D_Hailsham]

I'm going to try and move the relay box right to the top of the boiler house as far away from the boiler as possible. At the moment it is about half way up the inside (still about 1ft away from the metal housing of the boiler). The problem is the thermostat needs to be within about 6ft of the relay box to get a signal.

So you decided not to place the relay where the old stat was located. Why?

Could the batteries be an issue? I've used the batteries that came with the thermostat, although they have just been sat in the box for over a year. Would the battery power effect the wireless range?

Try another set of batteries!

it cuts out even if I move the thermostat 10ft across the kitchen! Ideally I want to place it in the lounge.

If you have several walls betwen thermostat and relay, you will get signal loss; the thicker the wall, the greater the loss. If the boiler house is attached to the house, it would be worth drilling through the wall and installing the relay inside the house.

 

[jonnyfonny]

The main reason for not locating the relay where the old stat was 2-fold.

Firstly, when I looked at the old stat it appeared to have a collection of black wires, and nothing seemed logical.

Secondly, when I checked the wiring into the boiler it appeared that only one device was wired in, and that was the timer switch. Very odd. The thermostat up in the bedroom (which was very old) must've been wired into their old boiler. So I figured I'd link out the timer and wire the relay box directly into the boiler. It was simple enough if a little uncomfortable, mainly due to access.

If push comes to shove I might mount the relay in the kitchen. The boiler house is built onto the side of the house, and the walls to the main house are quite thick (it's an old stone built house). Still, I can't believe it would loose it's signal so quickly over about 10ft of kitchen. I'll try a new set of batteries for starters, and then contemplate moving the relay box.

Thanks for the reply

 

[jonnyfonny]

OK. Just to update. I've put new batteries into the stat and moved the relay into the roof of the boiler house. Again the signal dropped out in the kitchen when I moved the thermostat to about 10ft from the wall the boiler mounts onto.

I also tested the range outside. So with nothing obstructing the signal other than maybe 5mm of plywood the signal didn't make 7 metres (roughly).

It's almost as if it should have an aerial and the aerial isn't working. Is the relay or thermostat faulty perhaps? I guess I could try my thermostat from my house to rule that out. Getting a little frustrated with it all. It's working perfectly apart from the range issue

 

[D_Hailsham]

I also tested the range outside. So with nothing obstructing the signal other than maybe 5mm of plywood the signal didn't make 7 metres (roughly).

That would suggest one of the units is faulty. Honeywell quote an open air range of about 30 metres.

If you bought the set new from a shop (not second hand via the internet) you should take it back and ask for a replacement.

 

[jonnyfonny]

I did buy the set new. Unfortunately it was over a year ago (and from ebay).

I've just taken my thermostat round from my house to eliminate it as a suspect! I paired it up (binded it) and did the range test again. It was no improvement whatsoever.

I'm beginning to think it is either:

A: the relay is faulty in some way
B: my wiring is a bit suspect

If it was my wiring which was a bit dodgy I would assume the unit would fail to operate completely? Obviously that is not the case as it works over a very short distance.

Does anybody know if you can buy the relay box on it own? Can't seem to find them anywhere. And Honeywell only offer tech support to registered installers so I guess they won't be willing to help

 

[snb]

you can buy the bits independantly but it's worth trying to manually rebind the unit with the receiver.

This will give it a new code.(sometimes existing equipment in your home or a neighbours could be operating on a very close frequency which can cause the problems)

I fit a lot of these units and they will communicate through 6 or 7 walls and still manage over 15m distance.

Don't use rechargable batteries. They will work for a few mins but then the voltage drops too low and you will get some very erratic communication.