DIY Doctor

Fitting an External Expansion Vessel to a Vaillant Boiler

Postby dannyj1984 » Fri Jun 07, 2019 8:22 pm

Good evening.

We had an annual boiler service today and been told the expansion vessel is knackered (water leaking out of the valve). The boiler is a Vaillant and about 10 years old, so don't really want to pay the quoted price of £350 for a replacement internal expansion vessel. There is an option of an external expansion vessel which is much cheaper and I can buy and fit myself I believe as there is no need to open up the boiler, just need to cut into the water and plumb in the new one. The boiler is in our utility room so space isn't an issue. I am pretty confident with doing this, just wanted to check if anyone could advise if any other gear is needed except for the expansion vessel? From research online 12L should be fine for our house, 3 bed semi, 7 radiators, no fancy underfloor heating etc.

Many thanks

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Simply Build It

Postby htg engineer » Fri Jun 21, 2019 9:39 pm

Google the boiler, it'll tell you the expansion vessel size. A good rule of thumb is 1l per radiator.

Tee into the return, close to the boiler and connect vessel.
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