Worcester 20/25 oil boiler losing pressure no hot water...

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I'm just looking for any ideas please before I call the engineer out again...

Worcester combi boiler started losing pressure, so topped it up again and all ok we had hot water again. However over the last week the pressure keeps dropping to nothing on the dial and not hot water. We have to keep opening the tap to get pressure but this is short lived. Engineer had a quick look yesterday on his way to another job and couldn't see any obvious leeks but it was only a quick look.

Woke up again to no pressure... any ideas before he comes out again.

Thanks in advance
 
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I'm just at DIY level, not a pro, but I know a little bit about my own oil fired WB heatslave.

The water must be going somewhere. It's either a leak on the central heating circuit, the PRV (pressure relief valve to outside), AAV (air vent inside boiler), the expansion vessel is filling with water, or the heat exchanger is letting water pass from heating to hot water circuit.

I would think the AAV leaking would be obvious, the PRV passing fairly obvious, (but you could tie a bag under the outlet in-case it's just letting go occasionally). If it's been going on for a while then it's probably not the expansion vessel (otherwise it would be full already). That just leaves a leak somewhere. If the pressure drop is quick enough, I would think you should be able to rule out a heat exchanger problem by seeing if the pressure drops quicker if a hot tap is left to run (you could do this with the boiler off, no need to throw hot water down the drain)
 
Thank you... that's great. I'm not even a DIYer just looking for some ideas before the engineer comes back in the morning. Boiler is in outhouse so no obvious leak in PRV. No obvious water in boiler. I'm presuming he checked the vessel when he looked quickly yesterday. There is no water going to the radiators.

He did say it might be a leak in the pipework in the house but we have no water marks on ceilings downstairs, no obvious leaks above ground level on ground floor but pipes go into the ground. I suppose I just need to be sure he's covered all options with the boiler before I even begin to think about how I find a leak underground.

Thanks again...
 
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PRV outlet should be routed outside outhouse... so check there.
 

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