Replacing an insensitive room thermostat

[triturus]

I had central heating installed early this year, so comes with all the expected controls (TRVs on all rads except where the room stat is), 7 day separate CH and HW programmer, and a room stat. (It is a conventional rad CH and HWC system.) The room stat seems to be the thing that is letting down the whole system control. It is either on for long periods, or off for long periods, and seems to be very insensitive.

The room thermostat is a Danfoss RET230P (old style). It is positioned on a solid internal wall (first floor landing). The walls are usually colder than the air temperature and I think the positioning of the air vent of the thermostat (for want of a better term ) is too close to the wall so the thermostat is responding to wall temperature rather than air temperature. I'm on a very tight income so I have the heating on the minimum I can get away with, so getting the whole building fabric up to a nice temperature is not possible (all internal walls are solid, and groundfloors are concrete, so it is a slow response building), and very good control is essential.

I'm wondering what is best to replace it with. I had a Honeywell T6360B (or earlier model) in a previous house, which worked well, so am considering that. I notice from DIYnot's FAQs that some digital room thermostats are better, and had a quick look at the Honeywell DT90E, and like the specificatiion, but notice that it is a 2 wired thermostat, whereas mine is a 3 wired (not that I've checked inside yet...). Does that rule out the DT90E?

Also I'm wondering whether I should mount the thermostat on a timber pattress to reduce the cold wall effect.

I'd be very grateful for your advice/experience.

 

[mickyg]

what boiler have you got?

 

[triturus]

what boiler have you got?

Worcester Bosch 12/18 Greenstar Camray Utility System oil fired boiler. (Although I said conventional system, the HW is pressured, and the CH is a sealed system.)

 

[mickyg]

ok, so your restricted to generic products. You could try a roomstat with TPI, such as the honeywell dt92 which u mentioned or one of many others, they will normally be battery 2 wire stats which will be fine for your installation, just make the neutral redundant.

 

[triturus]

Thanks, Mickyg.

I've just done a bit of reading around and now realise why the old mechanical thermostats need the live/neutral as well as switching and the newer digital ones only need the switching (plus battery).

Your suggestion of a wireless one is also good, as it means that I'd be able to alter the position of the thermostat until I find the most suitable position. My neighbour with an identical house who had new central heating put in two years ago ended up changing his room stat to a wireless one last year and said he now has a much more controllable system, so I guess had a similar problem. Makes one realise just how important the finer detail of controls can be ...

 

[mysteryman]

You should get your installer to come back and wire the room thermostat up properly. As you say, an electro-mechanical 'stat needs a neutral as well as live and switched live. This is to supply the anticipator heater - the 'stat will then lead, rather than follow, temperature changes.

 

[triturus]

You should get your installer to come back and wire the room thermostat up properly. As you say, an electro-mechanical 'stat needs a neutral as well as live and switched live. This is to supply the anticipator heater - the 'stat will then lead, rather than follow, temperature changes.

I'll look inside the existing thermostat, now I know how it should be wired to make sure it was not wired incorrectly. The plumber did a fine job, the electrician, however, was a pile of pants, but that's another story ...