Refilling combi boiler powered central heating system

[Chris Learmouth]

I have drained my central heating system, which is powered by a comb

boiler, but am now having difficulty refilling it. All radiators ar empty and bleed valves open. Are you able to offer suggestions? I hav a sneaky feeling combi systems are not that easy to refill. Not a majo problem really as I am having a new condensing boiler fitted within th next two to three weeks so can probably do without heating unti then..but it is getting a little chilly in rural Bedfordshire! Appreciate any advice you can give. Thanks Chri

-- Chris Learmouth

[Andy]

Would you like to tell us precisely what difficulty you are having in refilling it? It's so easy that I feel slightly baffled as to what difficulty you are experiencing. You turn on the valves on the filling loop ( built in or add-on ) and pressurise it to, say

1.5- 2bar whilst looking at the pressure gauge, turn off filling valves, then bleed radiators, then repeat until all air is out ( you can open all bleed valves on the rads and rush around closing them off as they fill up and start leaking, but it's fraught, your walls will get doused, and you will have to get to the filling loop to turn it off pronto after the last radiator is full else the system pressure will skyrocket and blow off via the overpressure valve. )

Final system pressure should be about 1.5 bar usually.

Andy.

[John Rumm]

I assume you mean the system is a sealed system without a header tank? (The fact that it is a combi has no real bearing).

One of the advantages of sealed systems is they are simpler to fill than vented systems since there is no possibility of air locks.

You can find all the details you need here:

a quick summary:

The simplest way to do this is with two people. One to control the filling valve and watch the pressure, one to go round bleading the rads.

1) Close all the bleed valves. In one empty rad add the inhibitor.

2) Assign task to a valve operator: Watch the valve and keep adding water to maintain the pressure round about the 1 bar level.

3) work your way round the rads, starting with the lowerst ones in the system and bleed them.

Once done do a final check on the pressure - between 1 and 1.5 bar is normal. Job done.

See the FAQ for the one person version of above.