Generator to supply domestic boiler

[JohnD]

I'm a bit surpised nobody has popped up yet who has actually tried it.

 

[Jackrae]

It's got nothing to do with the house 'earth' as such
The flame detection system relies upon a minute ionisation current (microamps) that flows between the ignition electrode and the body of the boiler structure (which is normally earthed) The boiler structure is itself is indirectly connected to the live and neutral supply sysetm via it's internal electrical workings.
Providing you have a 'connection' between the boiler chassis and the invertor's neutral (or earth screen) you should have an active flame detection route.
A simple try-it-and-see test will confirm either way.

 

[GarethW]

Could you use a UPS instead ?
No getting the genny and extension lead out or resetting the timers on the thermostat

 

[Harry Bloomfield]

In fact, if you had a "TT" earth in your house (i.e. achieved with a local earth rod in the ground, rather than an 'earth' provided by your supplier) (which many people, like me, do have), then the boiler would presumably work - and I can't see what would be different from that if you were using your own generator and an earth rod.

True - maybe the manufacturers tech people just have a general answer that assumes a generator out put will be so unstable, it would damage the boiler? So the always answer is NO.

 

[JohnW2]

John - Thought about an earth rod but not sure how that affects the MCB and RCD trip.

I'm not sure what MCB/RCD you are talking about, but I can't think of any particular issue. In fact, if you used a generator without providing some sort of 'earth' connection in its output (e.g. by connecting the generator's neutral to the 'earth' conductor in its output socket (or even in the plug), then any RCD you had in the generator supply would not work as intended/required.

..... My guess is it would work if I made a permanent connection to the house earth and used the generator to supply live and neutral.

I agree. In fact, even when it were 'unplugged' the boiler would almost certainly still be connected to your house earth, by virtue of metal piping connecting it to other things (like main bonding, immersion heaters etc.).

Kind Regards, John

 

[JohnW2]

True - maybe the manufacturers tech people just have a general answer that assumes a generator out put will be so unstable, it would damage the boiler? So the always answer is NO.

Very probably true.

I don't know whether it is different with the new-fangled technologies, but with my ancient boiler, both the ignition and 'flame failure' (which, in my case, is just an old-fashioned thermocouple) work fine when I plug it into my genny, and that remains true even if (undesirable though that may be, for other reasons), the output of the genny is 'floating'.

In any event, as I've just written to the OP, the boiler will (at least, if he has copper plumbing) almost inevitably continue to be connected to the house's earth (via pipework), again even if the genny output were floating.

Kind Regards, John

 

[Harry Bloomfield]

I don't know whether it is different with the new-fangled technologies, but with my ancient boiler, both the ignition and 'flame failure' (which, in my case, is just an old-fashioned thermocouple) work fine when I plug it into my genny, and that remains true even if (undesirable though that may be, for other reasons), the output of the genny is 'floating'.

They now use an ionisation probe to detect the flame, which allows a tiny current to flow through the flame, to the casing/metal of the boiler. No current, no flame - or no earth to the boiler.

 

[JohnW2]

They now use an ionisation probe to detect the flame, which allows a tiny current to flow through the flame, to the casing/metal of the boiler. No current, no flame - or no earth to the boiler.

Yes, I realise that - but does that differ materially from my ('old-fangled') thermocouple which uses the metallic outer of the thermocouple 'tube' (which is in electrical continuity with the "casing/metal of the boiler") as part of the electrical path?

Kind Regards, John

 

[Harry Bloomfield]

Yes, I realise that - but does that differ materially from my ('old-fangled') thermocouple which uses the metallic outer of the thermocouple 'tube' (which is in electrical continuity with the "casing/metal of the boiler") as part of the electrical path?

I suppose it could do - both poles of the thermocouple have the possibility to go the the gas valve, isolated from earth. An ionisation probe has to use the metal of the case, burner, pipework as the other pole, with no way to avoid it.

 

[martygturner]

My combi works just fine on my little 1000w genny and has done with both an earth rod banged in and using a genny switch to wire the house TNS earth to the genny.

Has worked fine using main consumer unit and a mains isolator to prevent backflow.

 

[JohnD]

Has worked fine using main consumer unit and a mains isolator to prevent backflow.

Your isolation arrangements appear to contravene the Electricity Act.

 

[charliegolf]

I'm a bit surpised nobody has popped up yet who has actually tried it.

I have, with 2 different generators. I did the socket bit (apparently must be non switched?). Wouldn't work with either. I had assumed it was because of 'purity-of-sine-wave' issues rather than earthing. Worcester Bosch gas combi.

 

[charliegolf]

My combi works just fine on my little 1000w genny and has done with both an earth rod banged in and using a genny switch to wire the house TNS earth to the genny.

Has worked fine using main consumer unit and a mains isolator to prevent backflow.

Bit more description for the dimmies pleaseMarty.

 

[ericmark]

The problem is trying to write one size fits all answer. There are so many variations. I remember looking at a Honda generator and finding when switched to 230 volt it was 55 - 0 - 175 volt with earth connected to the centre of one winding, to have externally bonded neutral and earth would have resulted in a short circuit.

So step one is test the generator, and if you don't know how, then get some one who does, as all to easy to get it wrong.

The flame out device for a pilot flame is nothing to do with mains supply, you have those with boilers with no mains supply, the spark igniter however can be piezo ignition again no main connection or using some mains transformer.

Using the earth connection can be dangerous, I have seen this with portable traffic lights, where the radar needed 55 - 0 - 55 volt to work, and if the earth was damaged you could get a 55 volt shock from the traffic light head. They were all recalled.

Putting it simple the earth wire should not be used to carry any current. However there are exceptions, my radio earth wire is connected to the RF output of my radio, but this is not the same earth rod as used for the main house earth.