Potentially fried my wireless receiver? Advice needed.

Milex8

With winter around the corner, I decided to replace my Strom SSRTPR05 wall mounted wired thermostat with the tado wireless smart thermostat starter kit V3+ (with stand).

I live in a new build flat than came with a Strom thermostat, which just lifts off the wall and away from the circuit attachment. It has a 2 wire setup (from a 5 wire mains cable in the wall cavity, the other 3 wires being blue. grey and earth. Blue and grey were capped off, and earth was grounded to a metal backplate at the back of the wall cavity).

Live connected to the COM terminal, and a black wire to the NO terminal, with the other end to my Baxi Assure Combi Boiler switched live terminal (I would assume, I haven't looked inside the boiler). The Strom is battery powered and simply connects the COM to the NO when the room temperature falls below a certain degree, but is terrible at taking accurate temp readings.

I bought a cheap multimeter before buying my tado (just £8.99 from Amazon, but decent reviews). I was surprised to see that the live was reading around around 270v rather than the UK 230v standard. But I put this down to an inaccurate reading from a cheap multimeter that probably wasn't calibrated correctly.

I've had no issues with any other appliances in my flat, no blown fuses or circuit trips, and the Strom worked fine other than being terrible. So I went ahead and bought my tado.

I wired it according to the switched live wiring diagram. Brown to L, Blue to N, bridged wire to from L to COM and the black NC wire in the NC terminal. Powered everything back on, but nothing lit up. No sparks, no burn marks, no burnt smells. Just nothing, no LED's lit up. I took some readings. Live and COM were reading 270v, NC 0v, but Neutral was also reading 270v, but should have been 0v.

I took a reading from the grey wire, which was 0v, and thought maybe the grey was the true neutral, and the wires had been configured incorrectly. So I replaced the N with the grey, disconnecting the blue, powered back on, but still no LED's. I took a multimeter reading and was shocked to see readings across the board of just over 350v, at which point I powered off again and quickly disconnected and capped all wires.

I've emailed my landlord last night (I live in social housing, and they're notoriously useless), they have a legal responsibility to investigate and faults or hazards under the electrical safety standards regulations act (England) 2020 (I know how I must sound right now, but honestly, they are useless unless there's a legal obligation to investigate).

I have some questions for the community though:

1. Have I most likely fried my wireless receiver, or does it have a build in fuse I can check/replace?
   
2. Can I request a replacement receiver under warranty once I've had the issue properly looked into and fixed, either by my landlord or most probably me having to hire an electrician.
   
3. Any ideas on why I might have been seeing readings of 350+v?
   

Thanks

Milex8

I had an inspection this morning.

The live wire from the cable inside the wall was 240v, the NC was a switched live livre, but the blue neutral and random grey wires were not grounded. So why were they there? The electrician assessed they were either just dormant or additional switched live wires. But the presence of a standard blue neutral wire giving off 0v led me to believe the cables were configured to support a live 230V circuit, but that wasn't the case. I was also wrongly using the NC terminal as a neutral point for the multimeter which was giving incorrect higher than expected readings. And replacing the blue with the grey (assuming it might be the true neutral) gave the 350+V readings, for which there's still no explanation.

Long story short, the wall wires are safe as long as they remain capped, and the power I'm using from a 5 amp plug socket is providing correct and safe voltage, and the tado is running fine. But I need to hire an electrician to further look into the wall wiring setup, assess what's going on and ensure I have a grounded neutral before I can ditch my plug setup and power directly from the wall.

policywonk

Those wireless receivers are usually robust and it is still possible that it works. However many things dont make sense. Please bear with me.

1. When you checked the voltage, did you set your multimeter to an AC reading, not a DC reading? If the meter was set wrong, it may have had to invoke its a safety circuit and read 276v instead of 240v. Strongly suggest you stop where you are, go back to the original mode, put the original stat back, the original cables where they were and prove to yourself that the boiler works. If it does still work, it means that when the mistakes occured, you did not blow the boiler's motherboard. If it doesnt work, you need to arrange a Baxi engineer call out. It is likely still under warranty.
2. Then, suggest you go back to Tado via the App, and ask for specific instructions on what Tado products for your specific boiler, which I assume is this: Freeboiler manuals Baxi Assure Combi pdf. Why? Because that boiler can operate in Opentherm mode which is more efficient, does not use mains voltage to switch and that mode saves money.
   1. The instructions from Tado should include how to wire the replacement Smart Wired Tado Stat to operate in Opentherm mode and how to get the other end fitted correctly to the boiler.
   2. Whilst waiting for an answer from Tado (may take 2-3 days),
      1. pause and properly trace those wires, behind that thermostat find out where they actually came from, likely somewhere either on the boiler or near it.
      2. If you dont know how to check that wiring, do get a sparkie involved and present him with the instruction manuals for both the Tado thermostat and the boiler. Should take no longer than 2 hours to fix this and have it ready to fit a Tado system.
3. Then consider this question. Why you need a wireless receiver for a combi. IIRC one only needs a Smart Wired Thermostat. Is there a reason why you elected to fit an extension kit, rather than a basic wired stat? Do you also have a hot water tank being fed by the combi?
4. In the interim, suggest you carefully dismount, repack the Tado products and return to the retailer, and ask for kit which Tado recommends, but only when you have clear instructions from Tado about the kit you actually need and how to wire it in and swap the parts.

Milex8

I'm a very cautious person, I looked up a YouTube tutorial on how to use my specific multimeter model before performing any tests, just to be 100% sure. So yes it was set to measure AC. I also studied the tado wiring diagrams so I was prepared for for installation.

Since posting this morning I have dismounted the receiver and connected it to a plug socket that I confirmed was outputting 240v, and thankfully everything lit up and synced. Luckily I have a plug socket directly underneath where the receiver is mounted, so I went out this afternoon to purchase a 5 amp plug and a length of standard 3 wire UK cable. The receiver is back on the wall, all wires except the NC wire are capped, and I'm supplying a confirmed 240v from the plug socket beneath the receiver, with the earth wire inserted into the terminal marked with a downwards arrow (it isn't labelled with a name on the wiring diagram, but I've seen installation videos where people have used it to earth the L and N connection). I've bridged the L and COM terminals so the NC is receiving 240v when engaged. I've tested everything with my multimeter and all the readings are correct and it's all synced up and working perfectly.

This is a temporary fix mind, until I hear back from my landlord to arrange an inspection of my in-wall wiring to assess the issues I originally encountered. Once all that is addressed and sorted I can wire it all back up and have a clean installation with no visible wires. So panic over for now.

But thank you for your comprehensive and detailed response. It's much appreciated :)

And technically I didn't need a wireless receiver, you're correct, but I prefer having the wireless stat in my living room for a more accurate temperature and humidity reading, given it's the largest room in my house, plus the old thermostat was in the hallway and not in the best position to take accurate temperature readings.

policywonk

@Milex8 The earth strap did go to the right place.
That multimeter recording 270v is a cause for worry. Please try and get it double checked. There may be a fault at your main distribution board.

hugbilly

I wonder whether you have two different phases from a three phase supply in your home, that might account further 300v + reading . . .

policywonk

@hugbilly Funny that. Our volunteer professional sparkie made exactly the same comment when he was over this week.

@Milex8. You said it was a new build. Often in a new estate they distribute the three phases across the estate and at each changeover point create a brand new permanant earth. If that multimeter does read 240v elsewhere, and given your checks, is unlikely that meter is wrong. You may have a remnant second phase affecting your property. It is important to have it checked out.