Viessmann Vitopend 100-W WH1B thermostat replacement

[jakub742]

Hi I bought MH1823 TuYa Smart Wifi Thermostat and i'm wondering how to connect it to my boiler.

Current thermostat wiring:

Vitopend schema:

I didnt check the cables inside the boiler, i'm not a professional just wondering if its possible. My current thermostat has only No and COM cables connected.
I'll appreciate any help thanks

 

[Madrab]

The stat you bought needs a permanent power - left to right - L&N, as well as the switching wires 2nd L and NO. The one you have looks like it's a really old program stat, it probably has it's permanent power connected internally somewhere else, probably at it's backplate and the COM and NO will go to the 2nd L and NO on the new stat.

What make and model is the old one?

 

[RandomGrinch]

it probably has it's permanent power connected internally somewhere else, probably at it's backplate

I would say it's battery operated, given the rather crusty battery terminals on the RHS!

@jakub742 , how simple would it be to run a new cable from the thermostat to the boiler?
As Madrab says above, if the thermostat has been wired to 1 and L on the boiler terminals, you also need to bring the N to the thermostat.

 

[jakub742]

This is connection inside a boiler.
@Madrab
So the COM will go to second L and No to No. I get that the new thermostat needs a power supply so i would use a separate power cable to connect Input L N.
Am i right ?
Not sure what kind of thermostat is the old one i was having trouble identifying it through google lens found few on marketplaces but without any name.

 

[RandomGrinch]

I'm not sure of the wiring regulations in Slovakia, but we in the UK would run a 3 core and earth flex from the boiler to the thermostat.
The brown wire would connect to L on boiler and L on the thermostat
The blue wire would connect to N on boiler and N on thermostat
The black wire would connect 1 on the boiler to NO on the thermostat
The yellow/green wire would connect to earth at the boiler and any metal backbox at the thermostat.
Finally a small link wire may need to be added between L and L on the thermostat - this might not be needed, but I haven't looked at the thermostat specifications yet.

 

[jakub742]

So you're suggesting that i move the blue cable to N that would connect to N in thermostat.
New black cable i would put into 1 (where blue is now) and connect it to No on thermostat.
I would also connect a green/yellow to earth on boiler and then to a backplate of thermostat.

Am i correct ?

And if i dont want to touch boiler to connect those new cable, can i use another 3 core cable that would go from separate socket electricity into input L N and also eath to backplate?
Then i would just connect Blue to to No as it is now and COM to second L

Does it make sense ?

 

[Madrab]

I would say it's battery operated, given the rather crusty battery terminals on the RHS!

oooo ... well spotted

 

[RandomGrinch]

I have just found the instructions - they recommend using the 'dry contacts' on the side for connecting to the boiler.

So the blue and brown wires in your existing thermostat could connect here.

And if i dont want to touch boiler to connect those new cable, can i use another 3 core cable that would go from separate socket electricity into input L N and also eath to backplate?

Yes, you could. Again, our UK regulations would say that the controls should be powered by the same circuit as the boiler, so there is a single point of isolation for both.

 

[jakub742]

Thank you very much for all the help
But sadly i have different issue with my boiler so i will postpone thermostat replacement

For some reason my boiler stopped heating the radiators, hot water running fine. A month ago when it happened i kinda played around with pressure, i drained few liters of water so it would be at 0, then put pressure to 1 it worked for 3 weeks happened again same trick didnt helped. I drained the entire water from the system opened the valves on radiators to drain all the water. Then i put all the water back bled radiators from air. Add water again to keep pressure around 1.5 when heating. Got ressurected again heating worked for a day. That was yesterday, just now it happened again. Control is on for heating, but it doesnt start. After few hours when i turn the heat button to max it starts making a sound like its working but after like 10 sec it will turn off.

Heating light is ON when thermostat is in heating mode, but it just not working. Hot water fine. So i studied on internet a bit, so as i understood it might be a diverter valve thats either not working or is stuck in hot water in taps or maybe a pump but i dont know.
No signalization of error like red blinking. Any suggestions ?

EDIT: I made a new thread for this issue:
Viessmann Vitopend 100-W WH1B heating not working. (Hot water in taps is fine)

 

[Madrab]

I have just found the instructions - they recommend using the 'dry contacts' on the side for connecting to the boiler.

Have a funny suspicion that may be the same case as a volt free connection but given it's not rated in the diagram I'd be a bit wary about sending 240V (SL) through that side of things TBTH.