Combi boilers and water pressure

[Rod]

Given the lack of available water in our reservoirs (as I write, rain is lashing the windows and side of the house), a thought occurred to me. Do any/some/all combi boilers actually require mains pressure in order to function as central heating boilers?

(Actually, the question should be whether any boilers require mains pressure to operate, but it only struck me in relation to combis. Please answer either variant.)

I can't help thinking that it would be pretty awful to have standpipes. To then also be unable to heat the house is just a bloomin' insult. Obviously, this is less of an issue during the summer for most of us but how far into colder autumn weather could the restrictions apply?

[Ed Sirett]

Some models might work with a running inlet pressure of as little 0.25 bar. Although the majority are looking for about 1 bar or so.

The primary side whether or combi or not will carry on working even if there is no mains water at all. However eventually the sealed system will needed to be topped up - but probably not that often. A conventional vented system would only need just enough to make up the losses in the loft header tank.

[Phil L]

They do require 'topping up' from time to time, but having the mains pressure permanently connected to them is never a good thing, unless you like seeing boiling water running down the outside wall.

[Andy]

Combis don't need mains pressure for the CH to work AFAIK. The central heating water is of course a sealed loop. I believe the combi DHW section senses temperature and flow, but not pressure.

Of course the CH loop is pressurised, probably to stop boiling in the primary loop, but often also as a side effect of supplying radiators that are often in the floor above the combi.

Andy