Adding external Wirless thermostat to Boiler

[RickH]

Been getting on with work on my parent's hose which they persuaded me to buy.

Heating system is standard single zone rads to a Baxi 105HE Condensing Combi boiler.

Checking out its all working - found the wall-mounted Honeywell thermostat had no effect on the boiler, the system, in fact, being controlled by the timer control on boiler and the heating temp dial on the boiler.


The system is under a service contract with British Gas (who did annual service & safety check in Jan) so called them.
They explained that separate thermostats are mandatory since 1982 so if faulty it would have to be replaced.

On inspection they found it was not wired in the boiler (yellow wire link across where stat would be wired) ... and no cable there, assume it must have been 'cut out' when the previous non-combi boiler was replaced 5 years ago. Honeywell stat certainly used to work with old boiler (simple bi-metal type)

I did ask how it passed the annual boiler & controls service if it doesn't work - no answer on that.

It would not be easy or neat to run in new cables .... so I have 2 options.

1. Fit a basic Remote wireless thermostat-anybody know of a simple one?, don't need programming options as there is a programmer timer on the boiler.
British gas are also preparing a quote, for this - though may do it myself.

 

[cross thread]

You can buy a wireless stat that is a straight forward fit It fits In the boiler to existing wiring and stat is wireless 30 mins to fit, look them up on ebay

 

[ianmcd]

center brand wireless stat is simple and easy to use, and not expensive, do not fit Salus they are rubbish

 

[gas112]

No room stat has got nothing to do with annual service and a105he is older than 5 years they went out of production end of 2011.
Have a look under boards by boiler the old rooms tat cable is probably been cut and pushed under there

 

[RickH]

Unable to pull boards up, kitchen was replaced same time as boiler ... so assume cut off and tiled over.

Hence easiest way is to fit a wireless unit.

 

[RickH]

center brand wireless stat is simple and easy to use, and not expensive, do not fit Salus they are rubbish

Is this a plug & replace for existing mechanical timer in boiler ... prefer that at boiler end rather than a separate wall mounted receiver.

I know this is not for 105HE, but this type ...
https://www.heatingcontrolsonline.c...mable-thermostat-for-combi-boilers-p-350.html

 

[gas112]

That will fit a 105he the plumb centre one needs wall mounted receiver

 

[RickH]

Is that a good make ... or is there another ‘first choice’

 

[ericmark]

separate thermostats are mandatory since 1982

Did not know that, but most central heating systems have thermostats at the end of each radiator, (TRV) so will likely be covered anyway law wise.

So first question is if the boiler modulates? If it does not modulate any thermostat will do, but if it modulates the thermostat either needs to also modulate, or have no anti hysteresis software which will switch boiler off/on as this will upset boilers built in system.

Not quite this simple, but idea is the TRV slowly reduces flow, and when too many TRV's have closed the by-pass valve starts to open so the return water slowly gets hotter and hotter and the boiler senses this and turns down the output to suit until at minimum output at which point it starts to cycle on/off and when the boiler controls the cycling it restarts at minimum output, so over the winter the TRV's control temperature in the most economic way.

However as warmer weather arrives, there is a problem, the boiler will continue to cycle all summer, so we fit a thermostat is a room without a TRV down stairs, with no alternative heating or outside door which is normally keep cool so as summer arrives it will switch off boiler, in real terms the room rarely exists, so we compromise and use the hall, which has outside door, so also fit a TRV so it can recover quickly after door has been opened, but of course the temperature of wall thermostat and TRV need matching.

With a modulating boiler if a wall thermostat starts to switch it off/on as it approaches the target temperature then it will stop the boilers algorithms working as designed, cheap wireless thermostats tend not to always fail safe, if they loose radio contact with receiver the boiler can stick on, the mid range tend to use mark/space anti hysteresis so mess up the boiler, so you need a smart thermostat which works out when to switch off, and then stays off for at least 1/2 so boiler algorithms can work, or connects to boiler ebus.

So it is down to how much automation you want, standard TRV will stop rooms over heating, and standard programmer will switch off heating while at work or in bed, however I found also the lock shield valve is important, open too much and the TRV will allow an over shoot specially if fitted on the return, and clearly closed to much and room will not get warm.

Stage 2 would be used programmable TRV heads, cheap eQ-3 start at £10 however the Wiser TRV heads claim to have a smart function where they work out and remember how long it takes room to heat, so can move room to a new target temperature faster than the cheap ones, which tend to have a long lead in, so moving from 16°C to 20°C up to 18°C is fast, but slows down 18°C to 20°C so it does not over shoot, I cheated and set to 22°C for an hour then back to 20°C and it did work, also the more expensive types connect to wall thermostat and internet etc, with functions like geofencing.

So stage 3 is something like Wiser, EvoHome, or Tado where the TRV's tell the wall thermostat when heat is required and in turn the thermostat tell the boiler. Likely looking at £600 plus for all the TRV heads and thermostat.

 

[ericmark]

I have questioned how much is saved both switching heating off when not at home, turning down in rooms not in use, and allowing boiler to actually extract the latent heat (Condensing) to my mind most important thing is for the home to be comfortable. When we bought the house we are now in there was loads to do, and spend money on, so I needed more TRV heads, but used cheap eQ-3 bluetooth (£15 each) instead of more Energenie which we had brought with us from old house. And I am rather pleased with the results. Non bluetooth you can get for £10 each.

The problem is if you latter want the TRV heads linked to the wall thermostat or able to use geofencing then it is £10 wasted, but I would think likely you would be OK with just fitting electronic eQ-3 heads, they work very well thermometer on desk shows 18.2°C and eQ-3 head set to 18°C can't really complain at that. And so easy to fit, no wiring, only thing I would say, if using the bluetooth with phone they will only connect to one phone. So I have some on my phone and some are on wife's phone. But you can manually alter them, one button changes from eco to comfort and you set the eco and comfort settings.

 

[ianmcd]

Did not know that, but most central heating systems have thermostats at the end of each radiator, (TRV) so will likely be covered anyway law wise.

you didnt know it because it isnt true, since the introduction of part L of the building regulations it is the case in England and Wales , and no a standard TRV does not count, you must have a boiler electrical interlock

 

[RickH]

All the rad have TRV .. the issue is with no ‘main Thermostat’ even if all roads close£ off as up to temp ... the boiler will keep cycling just heating up main feeds until boiler water Max temp reached .... which is wasted heat.

 

[ericmark]

All the rad have TRV .. the issue is with no ‘main Thermostat’ even if all roads close£ off as up to temp ... the boiler will keep cycling just heating up main feeds until boiler water Max temp reached .... which is wasted heat.

Yes having a thermostat to stop cycling is a good idea, Page 31 shows connections it will need thought as to where but no real problems.

 

[RickH]

Looking at that and a couple of install videos ... connection part is easy .... there is a link between 1 & 2. (No frost stat). So just remove link and wire in as per note ‘7’

 

[RickH]

Is the make :
https://www.heatingcontrolsonline.c...mable-thermostat-for-combi-boilers-p-350.html

It sorts of fits with it being Horstman looking at code, though I can't see manufacturers name anywhere.