The boiler: Glow worm 30 CXI Combi boiler

It is very important to install, maintain and clean out all heating systems properly, including the pipe work and radiators - read on to see what can occur if this is not done.

We went to a customer recently who had a serious problem with their 30 CXI  Combination boiler. The boiler would not heat up the domestic hot water supply nor would it  operate the central heating. After careful  testing out it was found that the diverter valve was not moving into the "hot water" position.

This can sometimes be cured with a simple addition of Sentinel X200 system restorer - a liquid additive, and then flushing the system clean. But that didn't cure this boiler. Further examination showed that the diverter valve central pin was seized solid -even when it was out of the boiler and on a work bench. In fact it was locked up so badly that even with pliers and grips it could not be moved! To cure this, all of the diverter valve was rebuilt with new Glow worm parts, and a new actuator [motor] was installed.

This did not repair the fault:- the hot water worked, but still not the central heating. It was discovered that the water was circulating though the by-pass valve. The old part was removed and on examination is was found that a spring had corroded and broken, so no pressure was available in the system [see pictures]. A new valve was purchased and fitted yet this also did not cure the problem. 

At this point we started to have self doubts, asking ourselves if the valve was put together correctly etc. etc. So we took the new actuator out of the boiler and tested if it was was moving far enough. It did not move at all [see pictures]. A new circuit board was needed.

So there were 3 separate faults on this boiler. These include 2 mechanical, water-side faults and 1 electrical fault.  All of this repair work was probably caused by a someone cutting corners- by:

• Not flushing the old system clean,
• Contractors offering the cheapest quote but not being able to complete their work correctly,
• OR even more worrying, the installer was not  CORGI registered nor competent to install this system in the first place.

Left picture - valve pin in hot water position - Right valve pin stuck in central heating position

By pass valve - spring broken