The customer is getting a low pressure E119 fault every day when the boiler is used. They top up the pressure in the morning and it’s gone by the afternoon.
This is a classic expansion vessel fault.
What is an expansion vessel?
The expansion vessel is a tank with an air bubble inside. (Red tank on the left). It uses this air bubble to keep the pressure in the system steady.
Over time (or if there is a fault) the air bubble leaks away and pressure in the system is no longer controlled.
What happens when an expansion vessel is faulty?
When the system heats up the pressure isn’t controlled so goes too high. It is then released by the safety valve. This lowers the pressure causing the E119 fault.
How do I fix a faulty expansion vessel?
The air bubble is reinstated in the tank using a bike pump.
When the bubble is back in the expansion vessel the pressure should stay under 2.5bar when hot.
For more help why don’t you check our pages on:
Low pressure with a Worcester boiler