Honeywell CMT927 Transmitter went bang!

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brummydave

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A Honeywell R6660D went bang last week. Must've sensed the coming drop in temperature! bad day explode

That's the RF Transmitter for the 927 programmable thermostat. (great bit of kit!) It had blown the central heating fuse (3A) shortly into the morning heating cycle, I could tell because the house was warm but all the controls and boiler were off. When I replaced it it blew almost straight away. Saw a flash from inside the box so disconnected the transmitter and bypassed the circuit. Back to just a programmer and TRVs at present.

Ever heard of anything like it?

The only slightly faulty thing this programmer has done is to lose its binding with the controls whenever there's a power cut. But rebinding has never been a bother apparently.

Anyone got a contact at Honeywell or elsewhere to get a replacement transmitter?

Or is there a likely fault somewhere that'd cause this which needs remedying first?

FYI All connections were tight, no sign of damaged cables or stress anywhere, the only bit of charring is on the prongs of the circuit board that go into the terminal block. And there's no smell of anything cooked.

Also, the motorized valve actuator was replaced not long ago if that's relevant!

TTFN

D.

 
lol! it's both. It's a standalone stat that can be used for many systems. the stat code is CMS927. it's not the stat itself that's faulty, it's the transmitter. and yes it has a line and neutral supply and a line and switched line control wiring.

i'll post a pic later.

 
not much can go wrong with them, I fit them all the time,

is it a NV or 230v contact?

you can get different ones that will fire the hot water, so a combi one,-like you have, cant control a system boiler properly, yours is only a single channel receiver.

still, never known them to go belly up like that, just make sure the boiler hasnt went pooh and is firing 230v out through the contacts if its meant to be NV.

 
yeah a plumber friend of mine only does honeywell and loves them to bits.

It's a 230v contact, it's been installed for a few months, it's a thermostat so is only designed to control a single channel - the heating.

The system is actually quite complex, it has a combi boiler providing instant hot water to the kitchen only and being used as a system boiler to three zones through a 3 channel horstmann progammer. zone one is house heating (ten rads up and down), zone two is under floor heating (kitchen) and zone three is an unvented megaflo cylinder for hot water to showers etc.

zone 1 has the honeywell stat, zone two has a siemens programmable stat (not as clever as the honeywell) and zone three has a cylinder stat.

I thought the honeywell was sparking like it did due to loose connections, but no.

So any other thoughts?

I'll try honeywell, denmans, cef, ebay etc for a repair or new transmitter but i'm more concerned what caused the boom!

 
Just had a reply from Honeywell. All this time I've been saying transmitter, whereas I meant receiver! doh! :Blushing

Anyhoo the good news is they'll send me a receiver... just cause I asked. Yay!!!

 
No help but I had a central heating system once that somebody else had wired that worked fine until the temp went down. It had a frost stat in the loft that some wally had wired the neutral in. The result was there was a short and it blew the fuse.

 
No help but I had a central heating system once that somebody else had wired that worked fine until the temp went down. It had a frost stat in the loft that some wally had wired the neutral in. The result was there was a short and it blew the fuse.
Blimey, that's actually useful to know. I was wiring a battery powered (2 wire) prog stat the other day and it did offer a neutral terminal for 'parking'. As I wasn't sure what parking was, I terminated it separately! Seems the need to be careful with unwanted neutrals is high.

---------- Post Auto-Merged at 23:12 ---------- Previous post was made at 23:11 ----------

Great news, a parcel from Honeywell came today with a new receiver in it! Interestingly the paperwork says CM67 room unit/HC60NG relay box, so I think the freebie is an old model. But hey, beggars can't be choosers, and this system will be a go go tomorrow. :D

 
Blimey, that's actually useful to know. I was wiring a battery powered (2 wire) prog stat the other day and it did offer a neutral terminal for 'parking'. As I wasn't sure what parking was, I terminated it separately! Seems the need to be careful with unwanted neutrals is high.---------- Post Auto-Merged at 23:12 ---------- Previous post was made at 23:11 ----------

Great news, a parcel from Honeywell came today with a new receiver in it! Interestingly the paperwork says CM67 room unit/HC60NG relay box, so I think the freebie is an old model. But hey, beggars can't be choosers, and this system will be a go go tomorrow. :D
why do you say old model brummy?

its only a 1 ch receiver, cant get much more basic,

the numbers dont always tally with old and new, just different things that do different stuff.

 
why do you say old model brummy?

its only a 1 ch receiver, cant get much more basic,

the numbers dont always tally with old and new, just different things that do different stuff.
I said 'old model as the CM67' was replaced by the CM927. The instructions I had with the new receiver referred to the older system. I guess the transmitter was upgraded but the receiver stayed the same!

Anyway, great news. The replacement went in without a fuss and the system's up and running efficiently once again.

Big thanks to Honeywell for an amazing service!

 

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