Smart TRV and room thermostat replacement

[michaelsage]

Hi,

A bit of background first I have a air source heat pump, downstairs is all underfloor heating and controlled by individual room thermostats. I am happy with this setup and can control this centrally (a heatmiser solution which I may add smarts to later). For hot water I have a simple honeywell st9100c controller and a schedule with an over ride option, again no plans to upgrade this (I use a switch bot to boost remotely).

Upstairs is where I would like to focus my efforts. I have 8 radiators, all in a single zone with a Honeywell CM707 controlling it, this is located on the landing and the landing radiator is the only one without a TRV. My proposal at the moment is to replace the TRVs on the radiators with smart ones, however, I am not sure what to do about the 707, presumably this is what "calls for heat" for the whole of the upstairs? From what I can work out from the manual and physically looking the CM707 has a live and switched live going into it.

At the moment I think I have a few options,

• replace the 707 with something that can be called by any of the smart TRVs (and add a smart TRV to the landing rad)
• replace the 707 with a smart room thermostat, allow the TRVs to call for heat and not add a TRV to the landing rad (there is no neutral so this limits my options)
• setup a schedule on the existing 707 and only allow the TRVs to call for heat during this time
• replace the 707 with a smart switch / relay and get the smart TRVs to switch the heat circuit on when they need heat

Is there anything else I could do? What products would I need to create this setup? What (if anything) is a direct smart replacement for the CM707.

At the moment I am leaning towards option 4... It seems to be the simplest solution?

Thanks!

 

[Deleted member 120897]

If upstairs is classed as a single zone, then it will likely have a zone valve, which is what the cm707 will switch on/off. You are correct in the way of live and switched for the cm707, so your options are:

• replace cm707 with another battery operated thermostat (not sure on smart type)
• replace cm707 with a smart wireless thermostat and receiver near the wiring center for the zone valve
• replace cm707 with a smart thermostat, but not sure whether this option can do the TRV’s.

 

[michaelsage]

If upstairs is classed as a single zone, then it will likely have a zone valve, which is what the cm707 will switch on/off. You are correct in the way of live and switched for the cm707, so your options are:

• replace cm707 with another battery operated thermostat (not sure on smart type)
• replace cm707 with a smart wireless thermostat and receiver near the wiring center for the zone valve
• replace cm707 with a smart thermostat, but not sure whether this option can do the TRV’s.

Thanks!

I think what I am going to do is replace it with a smart switch (sonoff do one that doesn't require a neutral wire) rather than a thermostat (I haven't had any luck finding a smart thermostat that will work without a neutral). I can then either pair that with a battery thermostat or just let the TRVs do the work.

 

[Deleted member 120897]

Plenty of thermostat’s work without a neutral, they just run on batteries, like the cm707

 

[ShaunCorbs]

As your on a heat pump
I would remove all the rad / ufh zones and leave it fully open and control the system via the unit controller eg room temp 21 set back at night to 18 ish

Your loosing efficiency in the system every time it starts and stops the heat pump you want them to run long

 

[michaelsage]

Plenty of thermostat’s work without a neutral, they just run on batteries, like the cm707

The only smart one I have found is the nest e. Happy to be corrected though!

 

[michaelsage]

As your on a heat pump
I would remove all the rad / ufh zones and leave it fully open and control the system via the unit controller eg room temp 21 set back at night to 18 ish

Your loosing efficiency in the system every time it starts and stops the heat pump you want them to run long

That's useful to know! I did wonder if the heat pump made things different. This is the first time I have had one. We just moved into the house and every room downstairs has a heatmiser controller for underfloor heating (even the cloakroom and utility room have their own).

Upstairs is a single zone with the CM707 and manual TRVs at the moment.

I am going to have it serviced soon and try and get a better understanding of how it all works / best practice setup / etc from the engineer.

Thank you!

 

[ShaunCorbs]

Is it a electric usage or more of a comfort thing your looking to add ?

 

[michaelsage]

Is it a electric usage or more of a comfort thing your looking to add ?

Honestly it's probably more of a comfort thing. We haven't had any of the downstairs heating on since we moved in! The house is pretty well insulated. The other night it was cold when we went to bed and it would be nice just to be able to boost a room or two for a couple of hours. The current honeywell doesn't allow boost for an hour or so, you can only do it until the next event, which isn't ideal!

 

[ShaunCorbs]

It might go over your head as it goes into designing and in-depth of figures etc but if you can have a watch of this

They’ve started to do a consumer set of videos there worth a watch also

 

[michaelsage]

It might go over your head as it goes into designing and in-depth of figures etc but if you can have a watch of this

They’ve started to do a consumer set of videos there worth a watch also

Wow! Well that was interesting and pretty enlightening! I can't pretend I understood some of it, but I got the gist even with the numbers.

For my next step I think I will have the system serviced and spend some time with the engineer work out what the best temperature / zoning (or not) etc for the house.

Unfortunately it looks like neither of the heat geeks registered in my area are around any more 🙁

Thank you for taking the time to reply