Regards my earlier ramble:

Imagine this scenario.

New build house with a combi-boiler that has wireless controls, the copper gas pipe does not have a Main Protective Bond because the supply is through a plastic pipe and the heating system has plastic pipework as well.

The homeowner buys an inverter generator and then disconnects the boiler electric supply flex from the installation and fits a plug to the flex to supply it from the generator.

The boiler will not run because the flame sensor completes its circuit through the body of the boiler and the earthing system.

So the home owner fits a neutral/earth link inside the new boiler plug.

Will the boiler run and if so why, conversely if not why; and will the boiler or generator be damaged doing so?

My take is that it is an unearthed generator and the Method of Protection is separation, so with this “neutral”/earth link installed the system is running under First Fault conditions, the boiler will run, but there could be 120 volts on the earthed metalwork of the boiler.

The illustration of the intended intended installation from the IET article could be this one, but with a “neutral”/earth link added, when there isn’t actually a neutral at zero volts, but two live lines at 120 volts with 240 volts between them, so the boiler flame sensor would see 240 volts between the line it is connected to and the boiler chassis.

Figure 5 Generator configured as electrical separation

Regards my earlier ramble:

Imagine this scenario.

New build house with a combi-boiler that has wireless controls, the copper gas pipe does not have a Main Protective Bond because the supply is through a plastic pipe and the heating system has plastic pipework as well.

The homeowner buys an inverter generator and then disconnects the boiler electric supply flex from the installation and fits a plug to the flex to supply it from the generator.

The boiler will not run because the flame sensor completes its circuit through the body of the boiler and the earthing system.

So the home owner fits a neutral/earth link inside the new boiler plug.

Will the boiler run and if so why, conversely if not why; and will the boiler or generator be damaged doing so?

My take is that it is an unearthed generator and the Method of Protection is separation, so with this “neutral”/earth link installed the system is running under First Fault conditions, the boiler will run, but there could be 120 volts on the earthed metalwork of the boiler.

The illustration of the intended intended installation from the IET article could be this one, but with a “neutral”/earth link added, when there isn’t actually a neutral at zero volts, but two live lines at 120 volts with 240 volts between them, so the boiler flame sensor would see 240 volts between the line it is connected to and the boiler chassis.

Figure 5 Generator configured as electrical separation