Generator to supply domestic boiler

[PetersDIY]

I have a 2kw sine wave generator and I want to get the gas boiler working during a power cut. I plan to replace the fused spur for the boiler with a standard socket and fit a three pin plug to the boiler (with 3A fuse), during a power cut I can unplug the boiler from the mains and via an extension lead connect the boiler to the generator which will run outside. Does this breach regulations? Is it safe?
Do I need to provide a separate earth supply for the generator / bolier?
Please note this is for rare but inconvenient power cuts I don't need a permanent installation with a change over switch and I'll only run the generator whilst I'm at home and not at night.

 

[ericmark]

I have asked the same question, and I have been told some boilers use the earth for spark generation, it seems only gas boilers do this, and I have an oil boiler, see this thread I started with same question.

I would not think there is any reason why it should not be powered by a generator or inverter, my boiler installation instructions say maximum power consumption 155 watt, but assume that will not include pumps, motorised valves, and thermostats. Mine is a Worcester Bosch Greenstar Utility 18/25 may be an idea if you say what boiler you have fitted.

 

[PetersDIY]

Thanks - It’s a Worcester Bosch Gas boiler not sure of the model it has an integrated pump. Given it currently has a 3A fuse total power consumption must be below 750W so the generator would easily cope with the power demand. Spark generation is a good point, hopefully someone will post who’s tried it before.

 

[securespark]

What did the manufacturers say?

 

[ericmark]

My attempt to measure inside the boiler current used did not work, too much needed to be dismantled, so did whole house.

So left meter 2.72-2.04=0.68 amp right meter 2.49-2.07=0.42 amp left meter newer and right meter jaws are stiff so will go by left meter, so 156.4 watts which seems to line up with the 155 watts the installation instructions say, plus pump and motorised valve.

I did repeat a few times in case some thing else stopped or started, I don't have a smart meter so I have to manually measure, I suppose these people with smart meters can clap their hands and get reading direct on their PC, the white box use to do that, but the batteries leaked.

As to what a gas boiler uses can't say, mine is oil.

 

[Harry Bloomfield]

I did repeat a few times in case some thing else stopped or started, I don't have a smart meter so I have to manually measure, I suppose these people with smart meters can clap their hands and get reading direct on their PC, the white box use to do that, but the batteries leaked.

I would make an estimate of a gas boiler needing around 10w, the much larger load will be the circulation pump.

The OP will need to ensure his entire heating system is supplied from that one fused spur unit.

 

[DetlefSchmitz]

Circulation pump about 35W.

 

[Jackrae]

An interesting question for which I cannot provide a definitive answer - however you might want to consider the following:-

Some flame ionisation type detection systems use the earth of the boiler as part of the detection circuit. For this reason they are 'polarity' sensitive ie the live and neutral mains supply for the boiler must be connected to the live and neutral terminals on the boiler.

You may therefore need to confirm that the neutral output of the invertor is somehow 'tied' to the invertor case and that this case is connected as the 'earth' within the supply socket.

 

[ericmark]

Last house the DHW boiler had no electrical supply, the CH boiler all the supply went through a 24 volt transformer, which was rather small, less than 50 VA, but mothers boiler as with my oil boiler has a fan that I am sure used more power.

 

[aptsys]

I would make an estimate of a gas boiler needing around 10w, the much larger load will be the circulation pump.

The OP will need to ensure his entire heating system is supplied from that one fused spur unit.

The fans on modern boilers are quite powerful, at full load often over 100W.

 

[Exedon]

Circulation pump about 35W.

That's a current pump even small domestic older pumps can be 95w or more.

 

[PetersDIY]

Have found the technical data for my Worcester Bosch Greenstar gas boiler maximum power consumption (boiler fan and integrated pump) is 109W so only the room thermostats and thermostatic valves in addition - a doddle for a 2Kw generator. The issue however may well be the earthing it would appear the boiler needs the house earth to drive ignition and flame failure - trying to find out more.

 

[PetersDIY]

Got through to a technician at Worcester Bosch today, the boiler needs an earth for the ignition and flame failure and would not work properly plugged in to a generator. Bottom line is it can’t be done safely. Thanks to everyone who contributed.

 

[SUNRAY]

So...
If the correct operation of the boiler relies on an earth connexion, than means there must be an earth current.
Unless I'm missing something fundamental, one only has to find the route of that current path and provide it in the new installation.

 

[JohnW2]

Got through to a technician at Worcester Bosch today, the boiler needs an earth for the ignition and flame failure and would not work properly plugged in to a generator. Bottom line is it can’t be done safely. Thanks to everyone who contributed.

As Sunray has implied, it can't be impossible, since there's nothing magic about your house's 'earth' that couldn't be effectively replicated with a generator supply - after all, even your normal electricity supply ultimately comes from 'a generator'. However, in order to do it one would need an understanding of the technicalities of how the boiler is actually using the 'earth' connection.

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.

Kind Regards, John