Can you fit aftermarket wireless thermostats to combi boilers?
Like is that what I think it is?

https://www.tlc-direct.co.uk/Products/SMTRT037.html

I fitted a Nest to ours, so I’m going with “yes”.

The one in your link should work, but “wireless” only refers to the communications between the programmer/thermostat and the receiver. The receiver still needs wiring in to the boiler. Depending on your boiler you may need to take the cover off to do the wiring, which exposes all the inner gubbins. If this is the case you’ll require a Gas Safe engineer to stay on the right side of the law.

Yes, if you look at the electrical drawings for your boiler you will see terminals to connect a thermostat, or in your case the receiver for your wireless one. The receiver may also require a 240v mains supply from somewhere, either a separate spur, or taken from the boiler itself.

Yes ours has one. Fitted it myself. Takes the live feed from the boiler itself.

A gas safe engineer??

An electrician would be my choice.

If taking the case off a boiler breaks the seal on the combustion chamber, which for some boilers you need to do to wire up the thermostat/programmer/receiver, you should be on the Gas Safe register. As long as the power supply to the boiler is already there, a Gas Safe engineer can do the wiring on the boiler (and should be able to, it’s only 4 wires – some don’t and get a spark in). A sparky on their own can’t take the case off a boiler to do the wiring (if that case forms a seal on the combustion chamber) unless they’re on the Gas Safe register.

Basically, if you have to undo screws to get into it then you need to be Gas Safe.

But.

The wiring must already be in place to a junction box for the existing thermostat and c/h controller.

All you are doing is replacing the thermostat and c/h controller with a ‘box’ that transmits in either bluetooth, zigbee or wi-fi to a wireless receiver c/h controller.

Don’t see any need to touch the boiler casing.

Like I said, an electrician.

Not necessarily. A lot of boilers just have a plug &play timer clipped in to the control panel with no external wiring. So if you’re changing that for something aftermarket the connections from the receiver to the boiler are generally inside the casing, e.g. wiring instructions for Worcester Bosch Greenstar

By all means call an electrician, but they’ll 99% charge you a call out fee just to tell you that you need a Gas Safe engineer.

Not all boilers will accept them.  Ours is an ACV one and you need some sort of adapter to make it work.  I think there is now a some sort of interface standard that most boilers use so if it is new it will likely work, but you should check before buying it

If taking the case off a boiler breaks the seal on the combustion chamber, which for some boilers you need to do to wire up the thermostat/programmer/receiver,

I’m not saying that there aren’t boilers where to access the electronics you need to open the combustion chamber – but that has not been the case on any of the half dozen boilers I’ve owned.

Basically, if you have to undo screws to get into it then you need to be Gas Safe.

That’s definitely not true. There are cases that screw on which do not form part of the “gas system”.

I’m not saying that there aren’t boilers where to access the electronics you need to open the combustion chamber – but that has not been the case on any of the half dozen boilers I’ve owned.

Whereas I’ve never worked on one the didn’t need the case off to access the wiring. Certainly every Worcester Bosch, every Ideal, every Keston and I think every Vokera.

That’s definitely not true. There are cases that screw on which do not form part of the “gas system”.

Maybe, not sure, see above, but either way it’s a good rule of thumb to work by if you’re not sure what you’re doing.

Look, I’m not saying that Joe Bloggs is incapable of installing their own wireless thermostat and receiver, I’m saying that if the case has to come off to do so and you can see gas valves and fans etc. then you need to be getting a GasSafe registered person involved to stay on the right side of the law.

Just fitted a Salus to our BAXI and basically what The Flying Ox says is bang on.