Generator to run oil fired boiler or immersion heater?

[Justin Time]

Hi. We've a champion generator, inverter, dual fuel, 3.6 kw, which we've used a couple of times during power outages over the last 18 months to power a fridge (class 1) - needed to keep my partner's meds. at fridge temperature and a range of other items (class 2) such as broadband router, TV, radio, a couple of standard lamps. Simple system, and the genny is a floating neutral earth.

But, aside from boiling the kettle on the oil fired Aga (runs without electricity when needed), or placing a kettle on top of the multifuel stove, hot water is a miss. We can live without it for a few days, but should we experience longer outages we'd like a hot shower, or two!

Generally, we're using an immersion heater for all our hot water (3kw) . We do have a circa 1973 oil boiler (Trianco Redfyre), but we rarely use this. It's run once a month for an hour to keep the system ticking over, and it's serviced every year.

Should we/could we use the genny to run the immersion heater for an hour or so to heat some water, or run the oil-boiler to heat some water? Which would be simplest to set up for a local electrician?

The hot water system is vented, and there are no pumps to the hot taps or to the gravity fed shower.

I'd like to avoid messing around with earths and keep the system floating if possible.

Thoughts gratefully accepted.

 

[James]

you will need about 2 hours to heat a 100L tank from 10 degrees to 60 degrees with the immersion heater.
at that time, it may be tight or even slightly over the rated output of the generator if you are running a fridge and tv etc.

rather than run the generator at full power for 2 hours, if it were me, I would run the boiler for probably an hour or less to heat the tank.
load on generator will be considerably less, so less noise, less fuel usage, lower risk of tripping out on over current.

However, most boilers use a single wire flame detector that requires the distributors N to be bonded to earth at some point.

when running on a generator, floating N is unlikely to trigger the flame detector and normally what happens is the boiler fires up but then shuts down quickly after that when it fails to get a flame detect signal in time.

I have in the past, changed the fused spur that isolates the boiler to a single socket and put a plug on the boiler flex.
this allows it to be plugged into the normal grid for most of the time but it could also be plugged into an extension lead powered by the generator.

it is worth trying to run the boiler from the generator as an experiment sometime (get the plug / socket installed first)

now a floating generator is ok to use for a single appliance because a L to earth fault will in theory make the earthed equipment the same voltage as the live but with no other reference voltage, there will be no shock if you touch an earthed case that has been joined to live.

but if there are more than 1 class 1 appliances (like a boiler and a fridge) if there was a fault with both appliances, a serious shock could happen if both were touched at the same time. bear in mind that the boiler will be bonded to all the pipework and radiators etc.

so, if you are running multiple class 1 appliances, a link at the generator between N and earth is a huge advantage to prevent danger. after this link an rcd should be installed (at 3.6kw a plug in rcd would suffice)
an earth rod in the location you normally have the generator sited would be a good addition, this could be connected to the generators earth point with a big crocodile clip if it is not permanently fitted.

My preferred approach would be a change over switch between the meter and the distribution board (fuse box)
output going to fuse box
one supply from the grid
one supply from an appliance inlet (16A or 32A plug that is mounted on the outside of the property)
in the inlet, you can join N and Earth together and also provide a link to a permanently installed earth rod.

 

[Justin Time]

Thank you James, that's immensely helpful. I've been mindful about only ever supplying one Class 1 item at a time, from previous advice (given on here I think).

So, if we ensured that we only ran the oil boiler, on its own, for say an hour, using the genny, via the single socket and put a plug on the boiler flex as you described, it would be a matter of seeing (an experiment as you explained) if the flame detector is triggered sufficiently. That seems like as useful first step - a good plan - and low cost in terms of investment. If it worked, the fridge would be fine switched off for that short a period of time the oil boiler is running.

 

[James]

Thank you James, that's immensely helpful. I've been mindful about only ever supplying one Class 1 item at a time, from previous advice (given on here I think).

So, if we ensured that we only ran the oil boiler, on its own, for say an hour, using the genny, via the single socket and put a plug on the boiler flex as you described, it would be a matter of seeing (an experiment as you explained) if the flame detector is triggered sufficiently. That seems like as useful first step - a good plan - and low cost in terms of investment. If it worked, the fridge would be fine switched off for that short a period of time the oil boiler is running.

Although i have given a like on the above post, I am not keen on the idea in general other than for a short duration test.
plugging and unplugging things to remain safe is generally a bad idea because it needs only one mistake to make things dangerous.

someone decides to plug another class 1 appliance in whilst the boiler is supplied and you could have a danger.

I would urge you to consider my preferred approach at the bottom of the last post.
It gives a far better standard of safety and doesn't require people to connect the right things at the right times.

 

[brianmoooore]

Every oil boiler I've worked on has used a photocell for flame detection. Even though your boiler is inefficient by current standards, as long as it is in reasonably good condition, it is a far less costly method of heating water than an immersion heater on a standard electricity tariff.