Combi Boiler losing pressure!


Old 10-19-11, 01:02 PM
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Question Combi Boiler losing pressure!


I have a 350 Worcester Combi Boiler.

For about the last 6 months I have noticed that the pressure relief pipe has been dripping outside my property whilst the boiler is on. I also noticed that the pressure has been running high (2.5-3 BAR) but the boiler has always worked ok. I presume this pressure is a bit high??

However, for the last 3 days, the boiler has not fired up (for heating on timer or hot water) due the pressure having dropped to zero. I am able to increase the pressure by turning a small black valve back up to 1.4 BAR and then the boiler fires. The pressure then climbs to 3 BAR and then works ok. When the boiler turns off (timer) and cools the pressure drops to zero again.

I have read my manual and it says to replace the control board. These appear to be quite expensive. Is it this that is allowing the pressure to rise too high? Also, I am thinking that my pressure release valve is probably ruined hence its allowing too much water to drain off?

As an aside, I had a burst pipe about 10 months ago and the pressure was lost in the system. A plumber repaired the pipe then re-pressurised the boiler as I have been doing by turning the black valve. I cannot be sure, but I think the pressure may have been running high since then!!!

Sorry for the assumptions/questions but badly need some advice - home is getting cold.

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Old 10-19-11, 04:21 PM
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Hi Tommo, most of us on here are on the other side of the pond and not really familiar with your heating appliances. We do things a bit differently here! ( surprise? no, I didn't think so! )

In any case, if your pressure is going to zero, then you have lost water in your system. I don't see where replacing the system board is advised. Why? It's doing what it should be doing, when the boiler loses pressure, the sensor is shutting the system down. That's all normal.

The reason that your relief valve is opening is most likely because the 'expansion vessel' in your boiler is waterlogged. These vessels are designed to control the pressure in the system by keeping an 'air cushion' which the water can push against as it is heated and expands. If the air charge is lost, that water has to go somewhere, and that means out the relief valve.

I don't know how difficult it is to get to this vessel in your boiler, or if it's even a DIY job... I'll see if I can find a manual for your unit on-line... but you might end up having to call the Engineers...
Old 10-19-11, 04:32 PM
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I suspect this is your combi?

This is a parts diagram. The pressure vessel is #32 in the diagram, but this parts list doesn't say much about it!

I find the user manual at the same website, but can not find installation or service manuals to be able to help further.

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