power to keep combi boiler working for water

The message from sm snipped-for-privacy@hotmail.com contains these words:

And the circulating pump, which is probably the biggest drain on the system. Probably, though you could get away with a UPS - they're much cheaper these days and it'd have all the bits in to do the "pick up and run" thing.

There's several on eBay.

Much more than that. I've got an invertor and car battery as backup for my fairly old boiler and that runs for at least 10 hours. I'd say the major consumer of power would be the CH pump. Without that the power consumption should only be a few watts - greater when valves etc operate.

Failing that a cheap generator can be had for £40+vat from places like makro.

sponix

You need to look at the type of inverter/UPS though - some have very poor output waveforms that may not work well into a significantly inductive load like the pump.

Fine if you don't have neighbours.

Don't you mean when they turn up with their extension lead and a hopeful smile?

For very small generators, I've had good results with soundproofing enclosures.

Take 8 paving slabs. One on the ground. Two at either end, slanting, with a small (~5mm) gap between them. The other two form a box. You end up with two interlocking slanted \_\ shapes, on the base plate. Add several 12V/240V fans to suck air in one hole. Mortar it all up, and put cling film over the top, place the last slab on, on some silicon sealant.

A typical combi will use about 150W i.e. about 0.6A at 230V. The pump and fan being the almost the entire load.

The message from "Dave Plowman (News)" contains these words:

If yours is the only warm house in the row, the neighbours might well all be in your kitchen.

I would rate mine (850 Watt maximum) as noisy as my car engine with the bonnet open.

Dave

Most combis use the pump to circulate water round the (diverted) primary circuit so as to feed the plate heat exchanger. So the power use running HW is going to be much the same as for CH.

Yup. If you use a UPS there is less chance of having difficulty with flame sensing since you will still have a normal ground reference for the boiler. A line interactive one with true sinusoidal output is probably a good idea for inductive loads like the pump and keeping the electronics happy.

Note that you aren't actually allowed to assume that the supplier's ground connection is still working during a power cut, when generating your own electricity.

Yes this is very true... especially if you are on PME. You should still have some earth reference from you main bonding however in most places unless completely piped in plastic.

On 20 Mar 2006 03:21:53 -0800, a particular chimpanzee named sm snipped-for-privacy@hotmail.com randomly hit the keyboard and produced:

Dump the combi & get a hot water cylinder?

If power outages are rare then don't bother, as a kettle on the gas hob will be enough for a quick shave and wash and rub down. If rural and outages are common then you need to look at the problem deeper, like having a small backup genny. A separate CU with essential supplies, fridge, light, TV, CH, could be fed from the genny (could be a wheeled portable unit hung on the wall). A two way manual throw-over switch would switch from the mains supply to the genny supply, so no complications, as mains and genny supply never come into contact. A back up genny is around £100-200. The whole thing can be around £300, so no major discomforts. Also you can use the portable genny for other things.

Combis with integral unvented cylinders will store the hot water.

Sad but true.

This will depend on the make and model. Many models will have a fan assisted flue and many will run the circulation pump even when doing only DHW.

A few older models (e.g. a Vaillant Sine have a natural draught flue) Many Ferrolis and a few others don't use the pump in DHW mode.

Worst case will be under 200W or 0.8A @230 Vac In most cases the central heating won't take any more electricity to run than just for water.