Vaillant Boiler Pressure Going Too High

I had a job to do today on an older Vaillant Ecotec combi boiler.

The system pressure kept going really high when the heating was on. But when the heating cooled down, the pressure went really low and caused an F22 fault.

What Causes Boiler Pressure To Go Really High

This is a common fault on Vaillant Ecotec boilers and is caused by the expansion vessel losing its charge.

From the factory they?ve got a 1 bar charge, but over time they lose it, which causes the pressure dramatically to rise when the heating is on.

How To Fix It

The good news is it?s a simple job to fix.

On this one, I just drained the boiler (not the whole system) and put a track pump (like a bike pump) on the expansion vessel valve and recharged it to just over 1 bar.

See pic below:

I then just refilled the boiler, vented it and tested the system. It?s a nice easy job that shouldn?t take more than an hour.

What Else Can Cause This Problem?

Split Expansion Vessel

If you have another brand of boiler and not a Vaillant, there?s a chance that recharging the expansion vessel may not fix the problem because the vessel has split internally. If this is the case, you would need to replace the expansion vessel, not just recharge it. This almost never happens on Vaillant boilers though.

Faulty Filling Loop Letting By

Other causes of the pressure going too high on a Vaillant Ecotec are the boiler?s built in filling loop letting by. This is the part of the boiler that lets you top up the system pressure if it goes down. Sometimes these valves don?t close properly and keep letting water in the boiler.

This over pressurises the boiler giving similar symptoms.