Replace external expansion vessel Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Kinstowan]

My combination boiler drops pressure. I have been told that another expansion tank, fitted externally next to the boiler, will do the job. I am OK with the water side of plumbing but would like some advice on how to do this please.

[htg engineer]

The new pressure vessel needs to be tee'd into the return pipe of the boiler with 22mm pipe. The tee has to be as close to the boiler as possible, hope this helps

[AndyB]

You could check first to see if internal expansion vessel has lost its charge.Recharging might solve the problem

[johnb]

hi kinstowan if you have pressure drop on boiler then you have a leak in the system or pressure vessel, adding another p/vessel in addition to existing should not be needed if the system has worked in the past.
check existing p/vessel is not full of water on the gas side it has schrader valve on gas side if you depress this and water comes out its knackered. if air comes out it may need recharging recharge to 1/2 bar all the best john