Honeywell CMT927 wireless stat

[fred]

Has anyone else seen the Honeywell CMT927 wireless stat relay unit lose the plot after power cycling?

I've been working on a system with one and find that the relay unit is failing to recognise the wireless stat after powering down the boiler & controls for maintenance. Last time it worked if the temp was set using manual mode but failed to respond in auto and then sorted itself out the day later to work fine on auto too.

I've seen this on another CMT927 install in the past which sorted itself out after I did something minor to kick start it but I can't remember what.

Anyone else seen this?

I'm not viewing this as a boiler issue but for info, one's a Vokera Excell and one's a Worcester Bosch 24 , both combis. Boilers are out of the loop as I'm viewing the demand via the mimic LED on the relay box.

[YAPH]

I have several CM927s in installations I've done and, although none gets power cycled frequently AFAIK, I've never had this issue. Sounds like a bad 'un.

[fred]

I agree it sounds bad but I've had it on another install too.

The common feature in both is that for a period the systems were subject to repeated switchings on and off via a switched FCU so I wonder if there was something inductive (like a boiler LV supply transformer) kicking back on switching off and causing corruption of the EEPROM data in the relay box. Not something I would expect from a Honeywell but who knows, maybe time for a suppressor at the relay box.

On the current one I went back today and did a factory reset on the wireless box and a re-binding to the relay unit and all appears well. The other was an isolated occurrence but it hasn't been power cycled since.

The installs were a year apart so I'm not suspecting a batch problem.

I know a few have them here but none have reported problems.

Thanks for the feedback.

[Andrew Gabriel]

I don't know this one, but could it be a battery died somewhere, either in the remote, or backup battery to handle mains outages?

[fred]

In article , Andrew Gabriel writes

It's _the_ Honeywell 7 day programmable wireless stat.

The wireless stat batteries are good and following a factory reset and re-binding of stat to relay unit so it does imply some kind of corruption.

They claim, "EEPROM memory holds the user program indefinitely" but I can see that may be the wireless unit only and perhaps they have gone the dirty way of a battery in the relay unit which I suspect would be more susceptible to corruption than EEPROM. I would be surprised though, little EEPROMs are dirt cheap.

Now that's it working again I'm forbidden to dismantle anything to take a look, next time I'll pop open the relay box and report the findings.

[YAPH]

Well thank you, too: I'll watch out for it on the ones I've put in.