Worcester Bosch Greenstar 27HE Pressure Loss


Postby KimT » Sat Jun 01, 2013 5:44 pm

Hi Folks,

I'd really appreciate a second opinion on a persistent problem with my Worcester Bosch combi boiler, please. I need to get it right because it looks likely to cost me a few hundred to sort out, and the timing is really not good!

Basically, the system has been losing pressure at the rate of approx. 1 bar every 4 days or so. I keep topping it up, but know this will cause corrosion if I keep doing it.

Getting straight to the point: I think it is the boiler itself (i.e. the combustion chamber) that is at fault (It's about 10.5 yrs old). The evidence for this is that there is a constant dripping of water from the condensate pipe, even when the boiler has been completely switched off for more than 16 hrs. The dripping is very slow (there are consistently 2 drips about 8 seconds apart, then a gap of thirty seconds, then another pair of drips, and so on), but the rate of dripping does not vary with the time since the boiler was last run, so I think the drips come from a constant leak, rather than being condensate from the flue.

A bit of background: When I first noticed the pressure drop, I identified a slow leak from the diverter valve. Coincidentally, we were also having problems with the boiler not switching between hot water and central heating properly. Believing the two things to be linked (I don't normally believe in coincidence with plumping!), I changed the diverter valve and, while the system was drained down, re-sealed a radiator vent plug which had an extremely slow leak as well. While this fixed the hot water/ central heating switching problem, the pressure loss continued.

I have since cranked up the pressure to 2 bar and gone over the entire system (all compression joints, valves, vent plugs, etc) and found no leaks. I also turned off the boiler isolating valves (i.e. separating it from the system), and found that the pressure still dropped at the same rate, so the problem is within the boiler casing. With a bright headtorch I have checked every nook and cranny inside that boiler casing, when hot and when cold, and there is no sign or sound of a leak.

I have no reason to suspect the heat exchanger, and the expansion vessel seems to work exactly as it should (i.e. when the boiler is switched on, the pressure builds by about 0.2 or 0.3 bar, as it always has done, and then recedes again as it cools). We never get anything leaking from the pressure release valve (which, in any case, was fitted new, with the diverter valve).

So, there is my case for the prosecution!

But if anyone is able to say "You silly so-and-so, you've completely overlooked something simple....." I'll gladly live with the embarrassment and keep the however many hundreds it is for a new combustion chamber in my bank account!

If it is what I suspect it to be, I will, of course, be employing a Gas Safe engineer to sort it out (don't mind risking getting wet, but getting blown up..........!). I just don't want to be paying out for random other parts to be replaced along the way.

Any views?

Thank for reading my small essay.

KimT
KimT
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Joined: Sat Jun 01, 2013 4:52 pm

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Postby htg engineer » Sat Jun 22, 2013 6:31 pm

If there is a constant drip like you say then it is likely to be a split on the main heatex.

It's also worth checking the pressure relief discharge outside, make sure there's no sign of the valve passing, it doesn't take much to lose 1 bar and it could go unnoticed outside.


htg
htg engineer
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Joined: Tue May 22, 2007 5:22 pm


Postby KimT » Mon Jun 24, 2013 6:14 pm

Thanks very much for taking time to reply, htg engineer.

Think you were the only one on this forum to do so! Probably because my posting was too long, and most people lost interest!

Yep, in the end I went with the leaking main heat exchanger diagnosis, and booked Worcester Bosch to repair it. That was two days ago, and everything seems good now. Great stuff! Nice to have got the diagnosis right, and not wasted money on it.

Cheers

KimT
KimT
Posts: 2
Joined: Sat Jun 01, 2013 4:52 pm


Postby htg engineer » Tue Jun 25, 2013 4:41 pm

To be honest I skip the long posts too if in a hurry. The shorter posts tend to get more reponses :-)
htg engineer
Posts: 3193
Joined: Tue May 22, 2007 5:22 pm


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