Condensing boiler pressure dropping quickly

[bullethead123]

Hi all,

The boiler is approx 10 yrs old and, for maybe the last 3 of those years, it's been losing pressure (during the winter months only) such that I have had to re-pressurise occasionally -maybe 2 or 3 times a Winter. I put off investigating further until a damp patch appeared on a downstairs inside wall.
Putting 2 + 2 together (and possibly ending up with 5), I figured there was a leak in pipes to the downstairs radiators but have pulled up floorboards, inspected thouroghly and found nothing.
Latley (last week or two) the boiler seems to need re-pressurising every 2 days. This morning I went outside while the CH was on and found hot water dripping at a frequency of 2-3 drops/second from this spout

which seems connected (by a piece of 15mm pipe) to the oblong box at the RHS of the below photo

I switched the CH off and within minuets the dripping had also stopped. I then filled the bath tub and no dripping from the spout occurred.

Does this sound like an expansion tank problem?

Is the oblong box an expansion tank? I've noticed something that looks like a bicycle tyre valve in the middle of the oblong box. Is this relevent?

If so, is it a fix just to replace it the expansion tank rather than the whole boiler? and

Is this something that could be done on a DIY basis?

Chris.

some more photos:

 

[MeldrewsMate]

Chris, you may or may not be on the right track, but as you've opened the sealed case you have, according to the Gas Regs, transgressed (because the boiler casing forms part of the flue/chimney system).
In this case the only advice I can give is to call in a Registered Gas Fitter to resolve your problem,and to ensure its safety post-repair.

 

[Razor900]

Alternatively you could attach a hose to a drain off on the system.

Open it and leave it open

Then using the valve you've already identified pump the expansion vessel up to 0.8 bar

Turn drain point off. Repressurise the heating system and see how lucky you are.

If the prv holds you've had a result

 

[bullethead123]

Alternatively you could attach a hose to a drain off on the system.

Open it and leave it open

Then using the valve you've already identified pump the expansion vessel up to 0.8 bar

Turn drain point off. Repressurise the heating system and see how lucky you are.

If the prv holds you've had a result

Is this such a drain-off? It's attached to a rad on the ground floor, I would be draining the whole radiator system?

I've poked the needle of the valve and only air (no water)rushes out. Is this a good sign?