I posted a message a while ago about a faulty Valliant combi boiler, and got some good advice here. It seems the fault is with a DHW heat exchanger which is overheating. Engineer says there is sludge in it causing this overheating (needs a power flush) but also a leak in the system - nothing is apparent or obvious, no drips at all and only place where could be under floorboards is in dining room, not a big area, though still possible. Is there a way to detect a possible leak? How do I go about it? Cd radiators etc be at fault?
The only sure way of finding a leak is to go round all of the pipes and eiither feel for a wet patch, or see where the green corrosion is. If it is still leaking, however little, there will definitely be damp on the pipe.
I've too got a problem with the DHW heat exchanger, i took mine out 2 weeks ago to rinse it out, but it has started to cut out again occasionally, nowehere near as much as before, when the shower would run for 2 minutes, then go cold, hot again for 2 minutes etc. Now it'll last 5 minutes before going cold for 30 seconds or so. I would like a good solution to this problem, as it is near impossible to clear out mine, as it is so small, and any jet sprayed in comes out pretty quick as the holes are at 90 degrees, so no fast flow through it possible. Alan.
Green corrosion can just be flux left on the pipework.
If it's scaled up, you'll need to use a descaler. Buy a tub of Furnox DS3 from a plumbers merchant. You use to be able to get it in B&Q too, but I couldn't see it there anymore recently.
If the primary side is blocked with sludge, rust, and other debris, that may not be cleanable.
Are you in a flat? Ask to see room below your kitchen...
Is kitchen on ground floor? Look for leaky system drain under floor (That's where ours leaks, as the rubber in the drain c*ck is of the 'use once' variety, and the screw that holds it on is plain iron and disappears quite quick...)
Hmm, the DHW exchanger didnt appear to be furred up at all on both occasions it has been out. There was a light black coating (iron oxide, FE3O4?), but no lumps/limescale build up at all visible.
I put some cleaner into the rad circuit a month ago, then flushed it out yesterday, though the water wasnt particularly mucky, just a light black tinge when drained off, then virtually clear when flushed through - I used the filling loop to wash through, with the drain being at the lowest point, attached to a pipe to go outside. I ran it both ways by closing aternate taps on the rad that the drain was attached to, then did it again with both taps open.
I then ran the hot kitchen tap for 10 minutes or so, and it ran fine with no cutting out. Sorted, or so I thought. I then tried the shower, which again cut out the hot water after a few minutes. So it is looking like there is a restriction in the shower somehwere, that is causing the water to back up, overheating in the DHW exchanger, then temporarliy cutting off the burner until the DHW exch. cools enough to be re-lit. Well, that's my theory. I'll investigate further to confirm/deny my theory. Ta Alan.
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