Thermostat advice

[VictorDelta]

During the upgrade of our CH system last year, our eminently satisfactory Honeywell thermostat (located in the hall) was replaced with a simple Drayton type (the sort with a large circular knob on the front).

I have noticed, by listening to the clicks made by the bimetallic switch inside it, that it appears to have a 'spread' of about 2 degrees - ie once it switches on, the hall temperature has to rise by 2 degrees before the heating switches off.

Not surprisingly this means, particularly at this time of year when the temperature is close to the ideal setting, that the heating sometimes comes on for much longer than necessary.

I know I would probably be better moving the stat to say the living room but, for several reasons, don't want to do that. Instead I would like to replace the Drayton thermostat with one that will control the hall temperature much more accurately (perhaps one with a digital display too, although that is not important).

Can anyone recommend any suitable models please.

Many thanks,

V

PS Should have mentioned, current stat is fed by a 3 wire cable, + / - and switched. The power is only on when the boiler is on ie controlled by the CH timeswitch. This may limit my options perhaps?

 

[mrgas]

I like the Honeywell programable roomstat.
You set different temps for different times of day.
Easy to fit (if you know what your doing)
Easy to use.
Very accurate temp control.

 

[Agile]

If you get one of the better programmable stats like the Drayton range you can set the hysteresis yourself.

Its probable that the installer did not correctly set the heat anticipator in the stat.

Tony

 

[AlanE]

Its probable that the installer did not correctly set the heat anticipator in the stat.

In what way is it adjustable then Tony?

 

[D_Hailsham]

I have noticed, by listening to the clicks made by the bimetallic switch inside it,

Modern Drayton RTS thermostats do not have a bimetallic switch but a thermistor to measure the temperature. The click you hear is just the relay working. The differential should be less than 1°C.

Have you checked that it has been wired correctly? Live (from the time switch CH ON terminal) and Neutral must go to the L and N terminals; the switch live to the boiler connects to terminal 3.

 

[mogget]

Modern Drayton RTS thermostats do not have a bimetallic switch

Apart from the RTS-8 'combi stat' which is both mechanical and awful!

 

[D_Hailsham]

Apart from the RTS-8 'combi stat' which is both mechanical and awful!

Forgotten the Combi-stat was also called the RTS-8. That is supposed to have a differential of 1°C. Why do Drayton produce the Combi Stat when one of the RTS Thermistor stats can do the job?

Wiring still needs to be correct as the anticipator should only be in circuit when the boiler is alight.

 

[mogget]

Why do Drayton produce the Combi Stat when one of the RTS Thermistor stats can do the job?

They claim that it's suitable for two-wire setups - and it is, as long as you don't mind sweating and shivering on a repeat cycle

It surprises me that there's not a battery-operated version of the electronic RTS stat.

 

[Agile]

Modern Drayton RTS thermostats do not have a bimetallic switch but a thermistor to measure the temperature. The click you hear is just the relay working.

The differential should be less than 1°C.

As far as I am aware, the manufacturers design to a minimum of 1°C differential.

This is because they believe that a smaller differential, particularly in a small property, causes unecessary cycling.

Tony

 

[VictorDelta]

The type I have is a Drayton (Invensys) RTS1 Room Thermostat and I've checked that the wiring is correct. However, I can't see any way to "set the heat anticipator in the stat" - whatever that refers to?

I agree that the clicks I hear are probably thermistor and relay but, even moving the dial very slowly up and down, the differential is definitely around 2 degrees at least.

Finally, I see the programmable thermostats appear to be two wire devices. Presumably this means they are battery powered? If so, what happens when the battery eventually fails - does the house freeze? (Oh, and presumably you don't have to leave the heating 'on' 24/7 if you have one of these devices, so all the controlling is done by them, or do you?)

V

 

[D_Hailsham]

The type I have is a Drayton (Invensys) RTS1 Room Thermostat and I've checked that the wiring is correct. However, I can't see any way to "set the heat anticipator in the stat" - whatever that refers to?

The RTS1 does not have an anticipator, so you can forget about that.

I agree that the clicks I hear are probably thermistor and relay but, even moving the dial very slowly up and down, the differential is definitely around 2 degrees at least.

The mfr spec says that the differential for a RTS1 is <0.6°C at 4°/hour. whatever that means

Finally, I see the programmable thermostats appear to be two wire devices. Presumably this means they are battery powered?

Yes

what happens when the battery eventually fails - does the house freeze?

It will, if you don't replace the battery!

 

[VictorDelta]

Many thanks. So, assuming I need to replace it with a programmable, digital version, is there one you would recommend?

V

 

[mogget]

You could always buy another honeywell stat, if you were happy with the old one.

 

[Agile]

If you want to spend a little money then you can get a wireless programmable stat and place it in the living room.

The hall is the last place anyone should want to control the temperature unless you have your computer there and spend most of your time there.

Tony

 

[glasgowgas]

are you sitting in the hall Tony, on yer computer, at 2 am??????????????