Boiler leak issue driving me up the wall

[Cainan]

Ok working at a church, job was to change 32 thermostatic radiator valves.....easy
change a few taps ok.....easy
fix pressure drop on boiler.....not so easy

the boiler house is situated about 6 metres away from the church so the pipework goes under ground and then into the church.
pressure drop is pretty much top up to 1.5 in the morning by night it's sitting at zero.
Done the obvious things, checked pressure on expansion vessel which is all good
been under all the floor boards in the church all bone dry
checked prv over night with container under again that is fine
i then isolated the flow and return under the floor boards when it was entering the building so I was only testing from boiler to church under ground pipework and again pressure down at zero so I can pretty much rule the church out completely
not sure why I am writing this as I think I know what is required but just in case some one has any other suggestion thought I would come on here.
am I faced with the sad fact that we are ripping up the concrete base outside and digging to the pipes? No leak on boiler, no leak on prv, expansion vessel fine but there's a pretty major leak somewhere and that's the only place it can be......right?

 

[Howsie]

Right. <hands shovel & pic >

 

[Killy Bing]

Are the pipes in ducting?

 

[albatross]

You could try leak sealer.

 

[Cainan]

You could try leak sealer.

Killy Bing- no not pipe ducted at all of what I can see difficult to tell though if it is later on of course

Albatross I actually tried that, hope more than anything but knew it wouldn't seal it so that's not worked either

 

[IDCHAPPY]

You could try leak sealer.

Too big a leak for that I reckon. It's pishing out somewhere.

 

[Cainan]

Too big a leak for that I reckon. It's pishing out somewhere.

Yea I tried it, there was no chance was there just hope more than anything

 

[Ermintrude]

Get a cat and genny or even a oscilloscope and trace the leak with sound . Thermal camera will struggle with concrete in top.

I would mole it. You can mole / drill a hole faster than u can dig / backfill normally about same cost. Drill new holes and thread in a 225mm mdpe pipe, use this as a sleeve for the insulated pipes to pass through?

 

[albatross]

If its a straight run and large pipe you may be able to access each end and just push slightly smaller pipe down it and connect each end, no or minimal digging?

 

[armyash]

I'd be interested to read how this gets dealt with.

 

[Whyme]

is it a condencing boiler. cos if it is isolate the boiler itself and see if the pressure drops. possibly pin holed main hex going down condence line.

 

[IDCHAPPY]

If it's not in a duct and has just been buried in concrete then the pipework will be rotten.

 

[Whyme]

ive seen denso'd pipe 30 odd year old ripped out of concrete and been right as rain. good luck anyway sounds spicy.

 

[IDCHAPPY]

I agree about the denso part but I was meaning if it hadn't or there was a gap or something.
Interesting though

 

[Cainan]

Ok bit more news, went round again today to dismantle pipe boxing etc and found that the pipes are actually 2" steel ppies! They have linked onto them when boilers where replaced a few years ago. So they go through the wall in pipe ducting but about half a metre down shining down with a torch you can see concrete and god knows what happens after that. It then must go about 4 m then onto a bend where it then heads about another 4 m into the church. Now this is a nice grass area where talking it is solid concrete base and will be a nightmare to take up but I simply can't see any other explanation. I liked someone's idea on here of pushing pipe through original one but with the tight bend it just won't be possible, 15mm hep at an absolute push but that would mean inch at boiler to 15 then back to inch at the other end which isn't feasible. Someone suggested it could be the condensing pipe but it's not it's in a boiler house so can see pipework run down onto a bend then along the floor in a drain and floor is all bone dry.

As a one man band, I will do the work but think I'll take a lot longer than getting the big boys in!

nightmare