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