24v thermostat

Hi forum

In a bad move, I've bought an american thermostat (Nest) which operates on 24v and is not compatible with the 240v of my vaillant ecotec 837.

Anyone know if there is a way to get them to work (transformer?).

Thanks in advance

I can see in the Ectotec manual that terminals 7, 8, 9 are for 24v - hoping that I can use these?

I seem to remember this coming up before and it being pointed out that these are not suitable for UK type central heating.

In the UK we use water as a medium to transmit the heat through the house and use thermostatic radiator valves (TRV) to keep the temperature correct in each room.

In the US they use hot air so rooms are all kept at same temperature in a completely different way.

So although you may get the voltage problem solved it will still not work in the UK. We do have special systems which do all sorts like connect to alarm system and activate with phone call but they are not compatible with "Nest".

Return nest and purchase compatible thermostat!
This could be a case of wasting money in an attempt to save money!
What are they £70?

PrenticeBoyofDerry said:

What are they £70?

Click to expand...

And the rest!

$249 on the nest website, i'd imagine with VAT and shipping added on, you wont have much change from £300.

feridoun said:

I can see in the Ectotec manual that terminals 7, 8, 9 are for 24v - hoping that I can use these?

Click to expand...

Can't be done fella

EFLImpudence said:

//search.diynot.com/forum_search.php?all=nest+thermostat&phrase=&any=&not=&intitle=&forum_id=0&since=any&sortbytime=0&author=&search=Search+Forum&stype=0

Click to expand...

There seems to be lots of advice against attempting to use a Nest thermostat, but if you want to, I can’t see it being too difficult if you have a sufficient level of technical competence.

The Nest is designed to work with American 24V ac HVAC control systems. As you suggest, you would need a small transformer to supply 24V to the thermostat which should be powered from your boiler, or the boiler supply. You would then need a 24V ac relay on the output of the Nest that can provide 240V ac rated switching contacts to operate your boiler.

From having a quick look at American standard HVAC control wiring and referring to http://nest.com/installation/ it appears the connections to the Nest thermostat would be:
Rh - 24V supply from transformer
C - 24V common from transformer
W1 - Heating output to relay coil

As to whether the Nest will work with a UK radiator based system, you would have to find out. The W1 output from the Nest is heating demand, so whether that demand is satisfied by hot air or by radiators shouldn’t matter. It just depends whether the Nest’s adaptive control is clever enough to accommodate the difference. I have seen posts on other forums from people in the UK who have managed to use them successfully.

What would be the point of all that when suitable equipment and accessories are readily available?

Years ago we would have a single thermostat running the whole central heating system and we would try to throttle back the lock shield valve to get some where near same heat in each room but the only way it really worked was with hot air central heating where the air was continually circulated around the house. However if any of the ducts leaked then it became expensive to run so in the UK we went over to the TRV.

The TRV is now part of an integrated system the boiler monitors the return temperature of the water and adjusts the flame height to suit and even has anti-cycle software built in and the only use of the electric thermostat is to switch off the system in the summer months and even that is suspect as the running of the pump once a day stops it sticking.

However there are still some old systems around with no TRV's fitted and there is no reason why you should not use the "Nest". With my system the thermostat is 24vac it controls supply to gas valve leaving the pump running until the water has cooled.

So question must be asked what system is installed? But my son has central heating connected to the alarm and once alarm set the central heating sends signals to the wireless valves reducing the house temperature but not turning it off and a simple phone call on mobile sets it back to working temperature before he comes home and also the alarm rings mobile should some one try to break in.

It can even be set to answer door bell. Or he can assess from remote computer to adjust settings with SCADA control. This remote control is not only done in US it is also done in UK if you want to pay.

The problem with all these systems is repairing when it goes wrong. This is not just central heating but many other items in the home. I am sure Linux is far better then MS Windows but finding some one to fix it when it goes wrong is the problem.

This is why I have not fitted a new central heating package as I get older I will reach a stage where I can't repair it any longer and I want to be able to call some one to do it all for me. If the "Nest" goes wrong are you going to pay airfare from US?

Yes there are people on here who understand it but finding some one to visit your house is another thing.

I suggest the OP Googles Opentherm.

Lectrician said:

An interesting diagram.

Click to expand...

So the thing has a single connection to zone valves, programmers, room thermostats and cylinder thermostats?

All of which also have a permanent live?

Page 26 does give a diagram showing the three 24v cables. However to see how these are used one has to look at this PDF and it would seem the 24v supply is all connected with the ebus and uses a VR30 board.

This it would seem changes the speed of the pump and is rather complex and I would not want to mess with these connections.