Worcester 24i Junior RSF Combi Boiler Central Heating Problem - Boiler Cuts Out and Fault Light Flashes Help, advice and problem solutions on all aspects of home appliances from washing machines to TV's

[GAW]

I have a old 24i combi boiler that has developed a fault when the Central Heating is on. After aprox.20 to 30 mins. the boiler cuts out and the fault indicator light flashes once a second indicating that it has over heated. Allow to cool down and reset its works but fails after a period of time again. The DHW works fine by its self and with the CH on, but is of coarse affected by the overheating problem. The boiler pressure is set at 1 bar which it maintains fairly well but I have noticed that it appears to increase more than usual when in the CH mode to the point that the needle is almost out of the black region. Has anyone had a similiar fault.

[plumbbob]

It is normal to see a slight increase in pressure when the central heating warms up but this should not be excessive and suggests the pressure vessel is faulty or needs repressurising.

[GAW]

Thanks for that information, I will check the pressure vessel's pressure. If the pressure vessel is faulty would the system maintain the 1 bar pressure that it appears to be holding. My immediate thoughts are that the only fault that can occur with a press. vessel is that the diaphram developes a leak, an I correct. Please let me know.

[plumbbob]

If the pressure vessel is faulty would the system maintain the 1 bar pressure that it appears to be holding.

Quite likely if the vessel has at least some pressure in it. As long as the relief valve isn't activated then the pressure will return to 1 bar when cold,

My immediate thoughts are that the only fault that can occur with a press. vessel is that the diaphragm develops a leak, am I correct. Please let me know.

No. Not necessarily. Vessels can lose pressure over time for a variety of reasons. The valve can leak for example. You wouldn't think twice about having to replace air in a car tyre would you?

If the PV has failed, yes, the diaphragm is the most common fault, but there wil be no external evidence as the leak is internal.

[GAW]

Hello Plumbbob. I checked the expansion vessel and it read 0.5bar which according to the manual is the factory setting. There are also other figures mentioned but they confused me. I considered the overheat thermistat being faulty so checked the electrical continuity of it as stated in the manual and that was fine. I fired up the boiler setting to a high central heating temp, let it run for approx.15 mins. and then I lowered the temp.gauge and the boiler cut out displaying the flashing light proving that overheat stat is sort of working, but it could be closing down prematurely.

[GAW]

I think I might have found the problem, as I started the boiler up again I heard noises from pump resembling air in system. Even though the radiators did not not need bleeding, I checked them first so I decided to vent the pump. A little air was released and now the boiler pressure when hot has only increase by appox. 0.6 bar and it's no longer cutting out. (Crossing fingers). Raises a question as the pump is ment to be self venting, why didn't it? Also for future information when should rads be bled - when hot or cold.
Thanks.