STOP
You should not have removed the casing from your boiler - that is for Gas Safe Registered Engineers only. It forms the safety room seal and your boiler should not be operated again until the Regulation 26.9 checks are carried out to ensure your safety. Your wiring looks OK, if a little scruffy, although it's a shame you're fitting an on/off room thermostat to an OpenTherm compatible boiler - an OT control would have made it more efficient
Flounders and Swan did a song about that, "And it all makes work for the working man to do." when doing an EICR the electrician has to inspect the electrical connections so clearly the electrical connections must be outside of any sealed systems as he needs to inspect, the manufacturer would need a recall to modify the boiler if that was the case. I am not Gas Safe but I have worked with flame proof equipment throughout my career and you do not use stuffing glands and standard PVC cables for flame proof enclosures, any electrician would flick to
page 32 of instructions to see how wired, main point is what type of RCD is required, there is nothing to say on the instructions that it needs to be connected up by a multi-skilled tradesman.
Installation instructions said:
A. Electrical Installation1. Checks to ensure electrical safety should be carried out by a competent person.2. ALWAYS carry out the preliminary electrical system checks, i.e. earth continuity, polarity, resistance to earth and short circuit, using a suitable test meter.
An earth loop impedance meter is expensive and its use can result in dangerous voltages being on the system, a competent person should have C&G 2391 for inspection and testing. Yes I know many people DIY and do electrical work without test equipment and do not follow the guidance in BS7671 on how to test it, but to be frank if everyone followed the rules, you may as well get rid of the electrical section of this forum.
I would agree if fitting a room thermostat may as well use OpenTherm if the boiler can use them. The instructions say
1.14 ELECTRICAL SUPPLY WARNING. This appliance must be earthed.Wiring external to the appliance MUST be in accordance with the current I.E.E. (BS.7671) Wiring Regulations and any local regulations which apply. For IE reference should be made to the current ETCI rules for electrical installations.The mains supply to the boiler and system wiring centre shall be through one common fused double pole isolator and for new heating systems, and where practical replacement installations, the isolator shall be situated adjacent to the appliance.
Clearly rather old instructions as it has not been IEE for around 14 years, BS7671 is a joint IET/BSi document, but a fused connection unit is considered as an isolator, so is a plug and socket. Things have moved on, using for example a Nest Gen 3 it is common to have multi power supplies, where the thermostat is supplied from separate supply to heat link, often using a USB plug and socket arrangement which is powered often from a different supply to boiler. But we would try to power the heat link from boiler supply.
The worry is that the system is not fully isolated when some one works on it, and in some cases we need labels
BS7671 said:
WARNING - DUAL SUPPLY
Isolate both mains and on-site generation before carrying out work.
Isolate the mains supply at ...........................................................,
Isolate the generator at.................................................................,
But this
is not permitted, and has not been allowed for any installation since 1966. That earth wire needs connecting even if the thermostat is class II, for an installation (not including portable appliances) an earth must be taken to the unit even if not used by the unit, yes I know plumbers and heating guys do flout the rules and I have even seen them use the earth wire as a live wire with tank thermostats, but that is still wrong, in the future some one may change the thermostat for one which needs and earth, and with people trying to persuade people not to inspect the wiring connections in the boiler, and a loop impedance meter is expensive so many DIY people don't have one, plus rules say earth must be provided, it is possible some one will just connect the earth wire without testing. Although 2 core cable would be wrong, at least no one would think it was earthed or bonded. The wire is there, so use it.
Yes it will work, but it will not comply with regulations or work in the most economic way.
