Danfoss 40704 thermostat not triggering boiler

BrendanMG

Hi all, 

Hoping that some wise person may be able to help. I have a Danfoss 40704 programmable thermostat (third picture below) on the first floor of my home, which is hard wired to the boiler. Downstairs I have a Danfoss TP9000MA-Si (4th picture) and Danfoss TS2 remote sensor. I can heat the upstairs rads independently and also the downstairs rads independently. The boiler IS NOT a combi boiler.

The Danfoss 40704 that's upstairs has stopped turning the boiler on. The display is still working and will show the flame signal, but the boiler doesn't fire up. The boiler is working perfectly as the ground floor rads are heating, controlled by the TP9000MA-Si, and I still have hot water. 

Until yesterday, the Danfoss 40704 used to emit a click sound when it turned the boiler on. It is still making a click, but the click is much quieter than it used to be, as of yesterday. I've removed the front cover and checked the wiring (2 wires) but all is fine. Any ideas folks? We have a 10 week old baby and the temperature upstairs dropped lower than is ideal last night as we had a hard frost. 

I include some pictures of the set-up I have. Any help would be much appreciated. Many thanks in advance folks. 

Upzeecreek

Needs new batteries! Ours is the same and had the same fault. Didn't indicate the batteries needed changing but that solved it. 

QrizB

The 40704 is battery powered? Have you tried changing the batteries?

oldernonethewiser

If it is battery powered then that is the likely source of the issue.  Had a relative's Danfloss which looked as if it was working but wasn't triggering the boiler. Replaced the battery and everything worked again.

Hope it is that simple.

ecraig

If the battery doesn’t fix it, turn your attention to those things that I have annotated in the pic.
they look a lot like danfoss HPA2 (without casing) and they tell the boiler to start or stop.
they are prone to breaking and can easily be replaced within 10 mins. The metal strip will stop going back and forth.
£40 quid on Amazon.

or it might be that the unit is sat inside some sort of heat shield…

sevenhills

BrendanMG said:

Until yesterday, the Danfoss 40704 used to emit a click sound when it turned the boiler on. It is still making a click, but the click is much quieter than it used to be, as of yesterday. I've removed the front cover and checked the wiring (2 wires) but all is fine.

When my central heating, which is similar to yours did the same, I replaced the thermostat. 
This one -

jefaz07

ecraig said:

If the battery doesn’t fix it, turn your attention to those things that I have annotated in the pic.
they look a lot like danfoss HPA2 (without casing) and they tell the boiler to start or stop.
they are prone to breaking and can easily be replaced within 10 mins. The metal strip will stop going back and forth.
£40 quid on Amazon.

or it might be that the unit is sat inside some sort of heat shield…

They look like Honeywell zone valves to me. 

ecraig

jefaz07 said:

ecraig said:

If the battery doesn’t fix it, turn your attention to those things that I have annotated in the pic.
they look a lot like danfoss HPA2 (without casing) and they tell the boiler to start or stop.
they are prone to breaking and can easily be replaced within 10 mins. The metal strip will stop going back and forth.
£40 quid on Amazon.

or it might be that the unit is sat inside some sort of heat shield…

They look like Honeywell zone valves to me. 

Yes, you’re right! Those ones are even cheaper to replace the actuator unit. Same process for swap over too…
(to be honest they are all very similar and mostly made by Honeywell, including the danfoss branded ones)

BrendanMG

Upzeecreek said:

Needs new batteries! Ours is the same and had the same fault. Didn't indicate the batteries needed changing but that solved it. 

Exactly that! The batteries were still illuminating the display so I didn't suspect they needed changing. Even more so because they were less than 6 months old. Clearly Panasonic batteries are utter rubbish. A new set of batteries did the trick, and my relief was immense!

Thanks all for your help. 

chrisw

I'm impressed that someone's actually gone to the trouble of painting all the pipe work in an airing cupboard silver!

Grizzlebeard

BrendanMG said:

Upzeecreek said:

Needs new batteries! Ours is the same and had the same fault. Didn't indicate the batteries needed changing but that solved it. 

Exactly that! The batteries were still illuminating the display so I didn't suspect they needed changing. Even more so because they were less than 6 months old. Clearly Panasonic batteries are utter rubbish. A new set of batteries did the trick, and my relief was immense!

Thanks all for your help. 

Not saying anybody got it wrong, but just a note to anyone.

Check the book, it almost certainly specifies Alkaline batteries (LR6).

Zinc carbon (R6, "Heavy Duty", "Extra Heavy Duty") will supply enough current to keep the chip and display alive, but after a few months use the volts drop (internal resistance) every time the wireless link tries to transmit.

(Buying the correct AA/AAA batteries is a nightmare. They all claim to be the best for this and that but the actual chemistry is often hidden in the code (LR03/LR6,R03/R06). Zinc will be attractively very much cheaper but cause the symptoms described here.)