Error 85

We had a lovely Easter Sunday lunch at Chez Pilou with Peter and Janice. But we arrived home to a cold house and "error 85" on the sensor for the central heating. I'm going to save you the details and give you the executive summary:  user manual in French only; discover secret menu on sensor and f**k up things even more; read French manual and restore original settings, still got the error code; switch off sensor, receiver and boiler, turn it all back on; still got error code; inspect wiring to receiver and discover poor workmanship and stray wires causing intermittent short circuit; return from basement full of hope, still got error code; suspect that room sensor and receiver have lost radio connection because of short circuit caused by the bad wiring; read French manual to no avail; spend half an hour doing detective work on the web and find English manual (different brand name, but same piece of kit); find out how to re-sync room sensor and receiver; error code disappears, boiler fires up, warm again.