Honeywell CMT921 room stat

[denvillesman]

Hi. I have just joined up having seen that the site has lots of users on plumbing heating. I am a humble DIYer. Can anyone help with a problem.

I have just been trying to wire up my new stat, ie the relay box which is a BDR91 (part of the CMT wireless kit). But I cannot get it to work and thus far no lights on either of the red/green LEDs, not a glimmer, so I guess something is amiss with the wiring. I am continuing to use the existing programmer.

I am trying to simply put the relay box in place of the exisiting old danfoss dial stat. The 4 wires to that are there are red, black, yellow and earth. I have put the red to L, black to N, and the yellow to B, and have put a link between A and the other L terminal. Have isolated the earth. That is my understango of what is needed, but am I missing something, OR is there something in the wiring at the boiler/programmer end that I should know about.

Any help gratefully received!!

 

[glasgowgas]

what boiler and system ya got?

 

[denvillesman]

The boiler is a Potterton Prima 100F and the controller is a Lifestyle LP522. Hope that helps.

 

[D_Hailsham]

The relay box is getting its power from the LP522 programmer, so that needs to be set to heating permanently on. A better way is to disconnect the wire from LP522 terminal 4 and connect it to LP522 terminal L. This bypasses the CH switch in the LP522.

 

[denvillesman]

I had ensured that the controller was calling for heat and had set it for on permanantly, but even with this no sign of any of the lights. Hope you can still help?

 

[D_Hailsham]

You originally said:

The 4 wires to that are there are red, black, yellow and earth. I have put the red to L, black to N, and the yellow to B, and have put a link between A and the other L terminal.

You have made the assumption that the colours have been used in the standard way: red=live, black=neutral and yellow=switched live. Unfortunately heating engineers have a habit of breaking the rules, so you can't rely on the standard. You need to check each wire separately, visually and with a meter. One of them will have 230V on it - that's the live - goes to L on receiver.The second will connect to an obvious neutral -connect to N on the receiver. The third wire will be the switched live and connects to B.

You also need to be wary of the "earth wire". If it is not connected to an obvious earth, it might be carrying voltage - another heating engineers' rule breaking whim.

If the wiring is OK, try using the same L terminal for the live and the link to A.

If that does not work, disconnect the receiver and wire it with a length of two core wire to a 3-pin plug. Plug it in and check the light comes on. If not it is faulty. You can also use this to check the communication between controller and receiver

 

[denvillesman]

Thank you so much for your ongoing help and we are progressing !

I have got to the point where the green light is doing exactly what it says in the instructions. I managed this by swopping the yellow and the black, neither of which has 240V bfore wiring it up, so that the yellow is now on N and the black is on 2. As I think you were suggesting. Red has 240V and is still on L.

But the boiler does not fire!

The stat and relay seem to be doing the business. With the stat on MAN if I crank it up calling for more than the actual temp the green light comes on on the relay and it clicks, and the flame symbol comes on on the thermostat - but no boiler. Conversley if I crank down the temp to below actual the green light goes off, it clicks and the flame symbol goes off.

Now, having had to put the old Danfoss back for now I tested for 240V. When wired up and with the controller NOT calling for heat there is 240V on red and black. When I call for heat there is 240V on red, black and yellow.

Please do you have any, hopefully final ideas.

I do very much appreicate you taking an interest in this. Thanks, John

 

[D_Hailsham]

I have got to the point where the green light is doing exactly what it says in the instructions. I managed this by swopping the yellow and the black, neither of which has 240V bfore wiring it up, so that the yellow is now on N and the black is on 2. As I think you were suggesting. Red has 240V and is still on L.

Told you the colours meant nothing

With the stat on MAN if I crank it up calling for more than the actual temp the green light comes on on the relay and it clicks, and the flame symbol comes on on the thermostat - but no boiler. Conversley if I crank down the temp to below actual the green light goes off, it clicks and the flame symbol goes off.

So the relay appear to be working OK. i.e the green light goes on/off. But is it putting 230v onto terminal 2? Check this with a meter.

If nothing on B, the relay is faulty. If it is OK, find the other end of the black wire and find out what it's connected to.

Now, having had to put the old Danfoss back for now I tested for 240V. When wired up and with the controller NOT calling for heat there is 240V on red and black. When I call for heat there is 240V on red, black and yellow.

Are you sure? Only two should have 230v, the live and the switched live The Neutral will be at 0 volts. You measure between neutral and the live wires.

 

[denvillesman]

Thanks for quick reply. To be honest I have until noe been using only one of those voltage testing screwdrivers (little neon display), but I have now dug out a dusty multimeter as well.

So what results -

So the relay appear to be working OK. i.e the green light goes on/off. But is it putting 230v onto terminal 2? Check this with a meter.

If nothing on B, the relay is faulty. If it is OK, find the other end of the black wire and find out what it's connected to

When the thermostat setting calls for heat the green light comes on AND there is 240V at terminal B on the relay. As tested with the screwdriver.

I am afraid I cannot possibly track back the black wire because there is no way I can establish where the thermostat cable goes to. For example the cable at the thermostat is flat T&E but all the cable going to boiler/controller are flex!! And all these cables just disapear into walls!

Quote:
Now, having had to put the old Danfoss back for now I tested for 240V. When wired up and with the controller NOT calling for heat there is 240V on red and black. When I call for heat there is 240V on red, black and yellow.

Are you sure? Only two should have 230v, the live and the switched live The Neutral will be at 0 volts. You measure between neutral and the live wires.

Well here I used the meter with the following results (this is with the old Danfoss in) -

With thermostat NOT calling for heat
across B/Y - 240v
across R/Y - 240v
across R/B - 0v (is that because both the B and R are live?)

With thermostat CALLING for heat

across B/Y - 22v
across R/Y - 0v
across R/B - 22v

These figures are what I am seeing and have been double checked. Hoping you can still offer some options.

 

[D_Hailsham]

When the thermostat setting calls for heat the green light comes on AND there is 240V at terminal B on the relay. As tested with the screwdriver.

Is the light going out and the meter reading 0V when the stat is turned down? If so the relay is working properly and it's just a case of finding the other end of the wire connected to terminal B

Do you have one 3-port motorized valve or two 2-port valves?

If you have one 3-port valve, the other end of the wire will connect to the same terminal as the white wire from the valve.

If you have two valves it will connect to the brown lead of the heating valve.

Well here I used the meter with the following results (this is with the old Danfoss in) -

With thermostat NOT calling for heat
across B/Y - 240v
across R/Y - 240v
across R/B - 0v (is that because both the B and R are live?)

Disconnect the Danfoss and measure the voltages on the bare wires. Only one pair should read 240V. They will be live and neutral. The third wire should be switched live.

Which model Danfoss stat do you have? The voltages are all wrong so I am wondering if it has been wired correctly in the first place.

 

[denvillesman]

I admire your patience D Hailsham, please hang in there!

Hey, I have traced the other end of the stat cable to a junction box in the airing cupboard, near the pump and a two port zone valve (ZV)(one pipe in/one out and either open or shut). Various cables into this box were in some trunking which when opened revealed one cable with the holy word "stat" on it. This is clearly controlled by the stat and remains shut until the stat calls for heat. I believe there is another two port valve in the loft by the thermostatically controlled HW cylinder.

Just one more thing, and my apologies for this, the current stat is not a Danfoss, but a Satchwell TLX 2356. I do hope that has not led you up any wrong paths.

So what about my latest tests - crikey this seems so complicated -

denvillesman wrote:
When the thermostat setting calls for heat the green light comes on AND there is 240V at terminal B on the relay. As tested with the screwdriver.

Is the light going out and the meter reading 0V when the stat is turned down? If so the relay is working properly and it's just a case of finding the other end of the wire connected to terminal B

I cannot get my meter probes up behind and into the terminals of the relay, but at the relay, yes when when the stat is turned down the green light goes off, the relay clicks and there is no voltage on terminal B with the voltage tester screwdriver. See later for meter tests done at the JB.

Before I say anything else I want to say what the connections are in this newly found junction box (JB), as there seems to me to be something wrong
Stat R - ZV grey
Stat Y - ZV brown
Stat B - not connected to anything at all

Remaining ZV wires go to -
white - not connected to anything
Orange - to some other wires in other cables!
Blue - to what seem like a clutch of other blue commons in other cables

Testing with the meter in this JB with the honeywell wired up I have following -
NOT calling for heat
R/Y - 220v
R/B - 0v
Y/B - 0v
Calling for heat
R/Y - 200v
R/B - 0V
Y/B - 200v

Having established the wiring is to the ZV (not the boiler) and going back to the Honeywell instrs, and having a further browse on the web, would I be right to wire up as follows -

Grey ZV to L relay via red in the cable
Brown ZV to B rely via yellow in the cable
Blue ZV to N rely via blue in the cable

 

[D_Hailsham]

What is the make and model no of the motorized valve?
Same for the valve in the loft.

 

[denvillesman]

The one in the airing cupboard by the pump and feeding into the JB I referred to is Honeywell F8-0032.
The one in the loft is Honeywell F2-0009. In fact there are two of these in the loft, one in each of the two primary flows into the TWO cylinders.

 

[D_Hailsham]

Honeywell F8-0032 ... Honeywell F2-0009.

Don't recognise either of those numbers. Honeywell valve numbers usually start with a V eg V4073.

If you can't see anything like that on the valves, can you post a pic of the valves?

 

[denvillesman]

I had just taken the numbers first quoted from what was stamped on the end of the bodies.
Having taken the covers off I see that the model numbers are V4043H1106 for the airing cupboard one and 272848 for the ones in the loft. I see from the internet that they are one and the same valve.