Expansion vessel issues on Worcester Bosch Greenstar CDI

How to check expansion vessel connection tube for blockages on Worcester Bosch Greenstar CDI boiler

I can’t remember why me made this video, but this is a short clip of how to check an expansion vessel connection tube for blockages.

This was done on a Worcester Bosch Greenstar CDI Combi boiler.

The expansion vessel on combi and system boilers is an extremely important part of the boiler.

If the expansion vessel isn’t working for any reason it will cause the boiler to over pressurise whenever you put the heating on.

It’s not so much of an issue on this particular boiler, but on some boilers the connection tube that connects the expansion vessel to the boiler can get blocked.

Once this tube is blocked it essentially makes the expansion vessel useless, as it is essentially disconnected from the boiler and system. There are a couple of ways you can check a connection tube If you suspect that it is blocked.

The first method involves adding some pressure to the expansion vessel then adding some pressure to the boiler. If you let the air out of the schrader valve on the expansion vessel the pressure on the gauge should drop.

The second method involves letting all the air out of the expansion vessel, then adding some pressure to the boiler. Then add some pressure to the expansion vessel with a pump and the pressure gauge on the boiler should rise.

Connection tube blockages are prone to certain models of boiler.

The Worcester Bosch Greenstar Junior and Si models of this generation(2005 – 2015) have an expansion vessel at the back of the boiler which is generally not easily accessible(depends on how flue is installed), with a connection tube that is prone blockages.

The irony is that the expansion vessel and connection tube on the CDI models are easily accessible but the connection tube isn’t prone to blockages on these models in our experience.