Sounds like the expansion tank is too small for increased volume of water in system now
What expantion tank this is a combi boiler?
Any time you heat water there will be expansion tank to take up any expansion of heated water
Please explain, where is the expansion tank is situated on this boiler and how would I fit a larger expansion tank as it must be integeral to the boiler casing.
Please explain as I cannot understand your last reply.
The tank is part of boiler and it may work just to replace it or have external one fitted