expansion vessel positioning

[dave]

Hi I am increasing the size of my heating system (loft convertion) and need to add another expansion vessel ( already 1 in the combi) I've managed to size the vessel requird but can't seem to get to the bottom of where to position it. I have been told that it needs to be as close to the boiler as possible but this is not easy for me space wise - it would be far easier to position it in the new upstairs. If it does need to be close to the boiler could someone explain why - i can't see the difference. Also should it be in the flow or return ( the 1 in the boiler is just straight off the tank) Any help would be gratefully received! Thanks

[Andy Hall]

I had to do exactly the same thing. The vessel in the boiler was probably just about adequate but I don't like marginal things, so added an additional vessel in the loft where the header tank for the original unvented system was located. I have the filling loop connection there as well because there was a convenient cold mains supply there, whereas their wasn't at the boiler position.

It doesn't matter if there is too much expansion capacity. You can calculate roughly on the basis of 10litres per 100litres of system capacity. If the existing one is working OK, then I would simply add in an 8 or 10 litre one and done with it.

[Andrew Gabriel]

It should be in the return feed near the boiler, but as you already have one there, I think you could put the extra one anywhere you like. The one in the boiler will cope with ensuring there isn't a momentary pressure drop at the sensor when the pump starts or a

2 or 3 port valve moves position, which might otherwise trigger a low-pressure trip.

[sheppy]

Thanks guys!

theres plenty of space in the eaves just where the pipes go down to the original system so I'll put it in the return there. Thats a relief - I had nightmares trying to work out how to get it close to the boiler when the boiler is fitted tightly into a kitchen cupboard! One thing I forgot - I take it it is just teed into the return pipe? Thanks again

[Andrew Gabriel]

Yes. I might include an isolation valve so you could change it in the future without draining everything down (although I didn't think of that when I fitted mine;-).

If you're shoving it in the loft, I would put it under the loft insulation so it isn't likely to freeze, although you don't want it hidden either.