CM927 relay clicking

[Markarina]

I'm trying to replace an old Honeywell chrontherm room thermostat, with a CM927. You move the set point levers on the old thermostat and the boiler fires up and the pump starts and the radiators get warm - perfect.

The old thermostat has 4 wires, brown (live?) blue (neutral?) black(switch) green/yellow(earth) I've wired up the 927 with brown and blue going into the NL, then a link from the second L to A and the switch into B. The wireless remote successfully flashes the green light on the receiver in test mode, try to run through the system test in the manual but all that happens is that the receiver unit click and flashes the green LED a couple of times and then nothing, no boiler or pump running, obviously the relay is not latching but I have no idea why not - any clues?

 

[D_Hailsham]

The old thermostat has 4 wires, brown (live?) blue (neutral?) black(switch) green/yellow(earth) I've wired up the 927 with brown and blue going into the NL, then a link from the second L to A and the switch into B.

Do you have an existing timer/programmer? If so the brown live will be fed from the Heating ON terminal of the timer. It needs to be fed from a permanent supply. You can get this either by setting the existing timer to continuous/always on, or by moving the brown wire to the L terminal of the timer.

 

[Markarina]

Pretty sure that this isn't the problem as the unit I am replacing is a very old chronotherm which as a built in analogue clock unit visible to the user and also seems to have a second non visible to the user timer unit, so the current unit must have a permanent live as it does not have any batteries.

 

[D_Hailsham]

Is it a brand new boxed item or an ebay type purchase?

Have you run through the test procedure and checked the binding?

Disconnect the relay completely and connect the L and N terminals to a length of cable with a standard plug on the other end. You can then test the stat independently.

 

[Markarina]

Yeah it's brand new and bought from Plumb Nation. Checked the binding by putting the display unit into test mode and the relay unit dutifully flashed every 6 seconds per the installation manual.

I guess this is a good time to point out this is the second unit I have tried, the first one was a chacon which after research we found was not a particular good brand so we assumed we had a faulty unit so we got the honeywell as a replacement. I've currently un-installed the 927 and put the ancient chronotherm back up which works without issue .... most fustrating

 

[D_Hailsham]

Honeywell products have a very good reputation for reliability, but no company can produce faultless goods 100% of the time.

If you wire the 927 as I suggested to a lead with a plug (no connections to A and B), can you replicate the problem?

If you turn the temperature up from min to max, at what temperature does the green light come on and start flashing?

Does the green light stay on continuously if you turn it up any higher?

 

[Markarina]

okay done that - checked the binding first which was all ok, then raised the set point nothing happened, so I then put it into troubleshoot mode which puts the relay on for 5 minutes this worked fine. So then went back to manual mode and it worked as expected raise the set point relay comes on, lower it relay goes off.

The one thing I didn't try when hooked up to the boiler was putting into the trouble shoot mode, so I'll try that later unless anyone else has a better suggestion

 

[D_Hailsham]

okay done that - checked the binding first which was all ok, then raised the set point nothing happened, so I then put it into troubleshoot mode which puts the relay on for 5 minutes this worked fine. So then went back to manual mode and it worked as expected raise the set point relay comes on, lower it relay goes off.

So the CM927 appears to be working OK.

The one thing I didn't try when hooked up to the boiler was putting into the trouble shoot mode, so I'll try that later unless anyone else has a better suggestion

That's a good idea, but I would do it with the Relay still plugged into the mains via the fly lead. This will enable you to determine if the fault is on the boiler side of the relay (fault returns) or in the supply to the relay (fault goes away).

 

[Markarina]

okay so put the relay box back on the wall (without the fly lead) when I put it into troubleshoot mode same thing happened relay clicks a couple of times but fails to latch. I'm slightly wary of using the fly lead as I'm slightly wary of having h two live wires not connected and floating around. Hopefully several layers of insulating tape should make them safe

 

[D_Hailsham]

okay so put the relay box back on the wall (without the fly lead) when I put it into troubleshoot mode same thing happened relay clicks a couple of times but fails to latch. I'm slightly wary of using the fly lead as I'm slightly wary of having two live wires not connected and floating around. Hopefully several layers of insulating tape should make them safe

Were the A and B wires still connected when you put the relay box back on the wall?

If so disconnect both and try again. If the clicking still occurs it will be a problem with the L and N connections; if it stops the problem is in the boiler connections.

What does the B wire connect to?

I understand your safety concerns.

 

[Markarina]

Yes A & B wires were connected, B is connected to what I am calling the switch wire, the live from the thermostat to the boiler. For reference I have a link from the second L terminal to the A terminal. I'll tape up the switch wire and give it another go over the weekend