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By avtur3
#1893314
Having a bit of a problem with our central heating thermostat, getting the heating system to switch reliably has been a bit of a problem since we moved in nearly 4 years ago.

The room stat is in the wrong position, it is in the lounge on the rear of the Aga's chimney breast, and because the Aga remains on 24/7 the temperature in the vicinity of the room stat is fairly constant. and doesn't reflect the temperature gradient seen in others around the house, at different times of the day, so we frequently have to intervene and manually swing the stat up or down.

Also the stat switches at different points depending on whether the temp is rising, to switch off, or falling to switch on; there seems to be about a 4 degree C variation in the switching temp.

I know I've seen a number of conversations here about smart controls for heating systems, does anyone know if any of the smart systems would interface with a simple two wire thermostat?
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By OCB
#1893322
avtur3 wrote:
I know I've seen a number of conversations here about smart controls for heating systems, does anyone know if any of the smart systems would interface with a simple two wire thermostat?


Tado - I replaced my late 1990s thermostat with a Tado one a few weeks ago. Start to finish, done in about 20 mins.

I also replaced all the TRVs to Tado smart TRVs...been an utter eye-opener in many respects; not least being how fast some of the rooms in my house lose heat/how much they demand heating to keep a temperature.

Feel free to PM me if you want
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By riverrock
#1893352
The variation in switching temp is normal - stops the system cycling too quickly.
With all of the smart systems (as far as I know) you replace a control system (timer, zone, hotwater controller) with the receiver, then the linked thermostat is wireless.
So you don't interface with a thermostat - you interface with the boiler & zone switches (removing the original thermostat from the system).

Does that make sense?
By riverrock
#1893396
A room stat will start/stop the boiler circulating hot water around that zone. The alternative is a smart valve on every radiator, and if none of them demand heat, the boiler stops circulating hot water, or a system in which hot water is constantly circulated when a time clock lets it.
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By PeteSpencer
#1893407
We have a roomstat in every room - Programmable' Heatmiser':which controls the underfloor circuit for that room (and radiator circuit for up stairs). There are IIRC 12 heating 'loops'.

. If no one's staying with us we turn off upstairs completely................... :wink:
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By rikur_
#1893587
riverrock wrote:The variation in switching temp is normal - stops the system cycling too quickly.

I believe the technical term is hysteresis.
In traditional systems I believe it used to be a simple 1 - 2 degrees.
Smart systems try to be cleverer with it in multiple ways:
- learning how quick your room heats up / cools down, and cutting in / out at times to try to avoid overshooting the target temperature;
- generally having slightly larger hysteresis than traditional systems, as boilers run more efficiently if run in longer cycles, rather than frequently cycling off/on. The Nest thermostat is particularly noticeable for this, particularly when you set the boiler type to 'oil';
- take into account the on/off times - i.e. minimise heating in the last 30 minutes of the 'on' time

These tricks contribute to their efficiency claims.
By Peter D
#1893588
Without going into Smart Controls, the below could be a easy fix for you!

If as you say, it’s a 2 wire room stat (live in from programmer, switch live out) it needs to be a digital room stat - these work on 2 wires and are very sensitive to temperature change e.g. Honeywell DT90E or similar.

If you have a mechanical non digital room stat these also need to have a neutral wire connected to activate the integral heat anticipator otherwise they suffer from the temperature lag you’ve described e.g. Honeywell T6360.
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By Flyingfemme
#1893627
In a previous house we replaced the old (very old) analogue stat with a wireless version. No programming, nothing fancy, but we could move the head to another room where it worked “better”.