How do I work out if I need an additional expansion vessel on a Condensing combi boiler?

The manual for the combi condensing boiler we have bought does not mention anything about fitting additional pressure vessels if specific circumstances apply.

There are 14 rads in total, 7 double panels with double convectors (type

22), 5 towel type radiators, one double panel single convector (Type 21) and a single panel single convector (type 20)

7 of the rads are on the upstairs zone, the other 7 on the downstairs zone.

Clearly the flow pipework has been duplicated twice in 22mm to permit the upstairs and the downstairs zoning arrangement and to allow for additional rads to be added should the house be extended so there is a lot more copper tube than usual.

Regards,

Stephen

Reply to
Stephen H
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Obviously, it depends on the size of the rads, but that *sounds* similar to my house. I did the sums (I'm surprised there is no "spec" in your manual) and decided that I needed the smallest additional vessel from BES, but in the end put in the second smallest (about the size of a watermelon) and this has been fine. For ease of checking and repressurising, you need an isolating valve between the vessel and the system, and a drain tap on the vessel side. When I changed the boiler I found that the internal vessel had failed without my knowledge. These are often very inaccessible and inconvenient to check, and are, I suspect, often neglected.

Reply to
Newshound

Does the boiler manual say what size of expansion vessel is included and/or what system volume it can cater for?

Do you know your system volume? This will expand by up to 2.5% between cold and hot - and the expansion shouldn't more than half fill your expansion vessel in order to limit the pressure rise to something sensible.

So, to give an example: System volume 100 litres. Expansion 2.5 litres. Expansion vessel 5 litres.

You should be able to work out from this whether or not you need any additional expansion capacity.

Reply to
Roger Mills

That does not sound like an excessively large system - given the towel rads are usually relatively water content in comparison to proper rads.

Try it and see what happens to the operating pressure. If it gets too high, create some temporary space by letting some air into a rad, and add another expansion vessel when you get the chance.

Reply to
John Rumm

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