Wired Volt Free Thermostat

[toml]

Hi

I have had a look at a job today where the customer has 7 battery operated volt free wired daily programmable thermostats in his home.

the problem is that on a couple of occasions, after he has come home from working abroad for a few months, the battery has gone flat on one of these stats which for some reason has sent the underfloor heating into flat out mode.

Obviously the customer doesnt want this and wants away with the batterys and wants hard wired stats, or something that he knows will last......and it has to have a dial, he doesnt like the fiddly little buttons on the existing.

ive had a little look into it initially thinking the batteries where to back up the times when the heating is not required (eg summer etc) but upon further research, i found that the batteries are operating the stat.

Imbetween the 2 connections on the stats i have 4.92V DC (obviously 3 would be coming from batteries)

What can i do?  ive found a horstmann stat which supposedly has a battery life of 2years but im not very clued up on heating systems, let alone volt free ones.

PS the stats at them moment are these ones.......http://www.amazon.co.uk/Celect-Digital-Programmable-Room-Thermostat/dp/B0077LO8L2

Many thanks

Tom

 

[ProDave]

ANY room thermostat will work.

You will find what he has at the moment are programmable stats, so he can set "on" and "off" times for the heating individually room by room.

These battery powered stats have latching relays, to save battery power. The downside is when the battery fails, the relay remains as it was, either on, or off, which can leave the heating stuck on. Not a big issue if you are in the house, but obviously a problem if nobody is there to notice it.

So you could put any ordinary mechanical thermostat, but you lose the programmability element of it. You might also have a problem with hysteresis if you don't have a neutral connection to work the accellerator heater (which wouldn't work anyway due to you switching low voltage.

I would suggest you try to find a mains powered programmable thermostat (but you will need to provide a mains supply to power it)

Or failing that, keep the programmable stats, but fit a second ordinary thermostat in series with it. Set the ordinary stat just a little higher than the normal set temperature, and it will then be there to catch it when the battery fails to stop the rooms overheating something stupid.

 

[Steve3948]

It may be 12/24 volt on the volt free contacts, from possibly UFH controller.

 

[toml]

thats interesting, i always thought mechanical stats needed a neutral to work. thats given me alot of food for thought now

 

[ProDave]

thats interesting, i always thought mechanical stats needed a neutral to work. thats given me alot of food for thought now

Mechanical stats will work on low voltage without a neutral, but may have several degrees hysteresis between the turn on and turn off temperature. The neutral connection powers a small accellerator heater within it to cancel out that hysteresis.

 

[toml]

end result on this, i have wired 7 digital 7day immersion timers into the circuit before the control gear and wired 7 mechanical thermostats, all is working, customer and me are both happy with it

 

[Doc Hudson]

Thank you Tom for giving us a concluding update. To many question threads get left up in the air and we never know if any advice given has been used or if a different solution has been found. Always nice to hear a happy ending. I will close this thread now.

Doc H.