Boiler problem expansion vessel

Dee44

Hi, I have been informed by an engineer who did my boiler service/certificate that its needs a new expansion vessel. However, he passed the boiler on inspection and didn't tell me about this until a week later. Can anyone please tell me what would happen if I don't get this fixed. Trouble is I now don't trust him because he took so long to let me know and don't actually know enough to know if the boiler needs this new part. It seems to be working ok and heats the house and water for my tenants but it is very old. Many thanks.

bridgedino

Does the boiler pressure gauge increase when the heating is on?

It's hard to comment on someone's diagnosis although the gap in telling you the fault should really be better explained by the engineer.

Often the expansion vessel just need re-pressurised rather than replaced

Ectophile

Assuming it's a sealed, pressurised central heating system, the expansion vessel is to allow the water to expand as it gets hot.

Normally, the pressure would sit at a specified pressure (typically 1 or 1.5 bar) when cold. As the system heats up, the pressure should rise a bit - perhaps by 0.5 to 1 bar.

If the expansion vessel fails, the expanding water has nowhere to go. Eventually the pressure gets so high that a relief valve opens and lets out some water. After that, you're into an endless cycle of topping it up when it's cold again, as the pressure drops too low as it cools down again.

This continues until the valve either sticks open (you can't pressurise the system) or it sticks closed (the pressure keeps going up until something pops).