Closed System Leak

[stevedo]

I have a Worcester Bosch R28 HE system condensing boiler, i.e. a "closed" system.

I think I have a leak in the system although there are no immediate signs of this. Without me using the bolier at all (use immersion heater for water, room thermostat right down so no chance of heating coming on) the system loses about 0.4bar over a 48 hour period i.e. goes from 1.0 to 0.6 bar as measured by gauge in the airing cupboard upstairs (filling loop also up there!).

There are no signs of water in and around the bolier or at any of the radiators/TRVs/lockshields and currently no damp patches on any ceilings. There are no signs of water outside where the "overflow" (not condensate) pipe for the boiler is situated.

I'm slightly confused in that although there appears to be a leak, when bleeding radiators I get no air out at all, just water. I would expect to get air out from somewhere if there were a leak?

A colleague at work suggested that there could be a leak in the water cylinder, I assume from the pipe that carries hot water from the boiler and through it to heat the domestic water. How could I check this and is that indeed a possibility.

The last possibility, and a really scary one, is if the leak is downstairs in the concrete floor. We have approx 170 square metres of wooden flooring and 35 square metres of tiled flooring in the kitchen. How would you proceed in finding a leak in this scenario if this was your place?

Any advice/guidance/sugestions etc gratefully received.

 

[ChrisR]

Is the tap water from a tank in the loft? If the coil's leaking, the level in the big tank will go up, but you'll have difficulty seeing it, as you wouldn't be able to use the water during your test.

It can be seriously difficult finding leaks. If you put the CH pressure at 1 bar and collect water out of a drain point on the boiler until it reads 0.6, you'll have an idea of how much water you're looking for. That will also tell you something about how much air there is in the expansion vessel.
The EV masks leaks - I've capped the thing off when looking for leaks - any water loss at all and the pressure collapses. For testing purposes you could put the pressure up to say 2 bar - to give yourself more to find!
You could close all your rad valves to help a bit (in finding the leak), and put valves in the pipes to the cylinder.

No you wouldn't expect any air in the system due to a normal leak.

A tale: I was putting a boiler on someone else's new heating system, which had been tested to 4 bar water with a proper pump. It showed a drop on the guage much faster than yours but we couldn't find it. So dug up the concrete to cut and cap the pipes, to test half the system at a time.

After the third dissection, we found a pushfit connection, buried in the concrete, which was the leak. The concrete, barely an inch thick over the fitting, was bone dry. The water seemed to be going down through a hole in the dpc underneath.

 

[stevedo]

Hi Chris,

yes the tap water is from a tank in the loft (via a water softener). What test would I need to conduct to determine if the leak was in the hot water cylinder.

I've determined that 1.0 to 0.6 bar is 1 1/4 pints. If I use either DHW or CH the rate of leak is higher (not measured).

I'm not quite sure how the EV works and therefore how it would mask a leak or where I would cap it off. Is this something I could do myself?

If I need to start excavating, where would I start or is this really something for the professionals?

Thanks for your help
Steve

 

[doitall]

Easiest way to test the cylinder is to turn it off via the valve and open the hot taps, when they stop running leave one open and pressurise the boiler, if the cylinder has gone the tap should start dripping again.

As Chris said take the pressure up to 2 bar

 

[Agile]

There are two other things you can do.

One is to put a small bottle over the "overflow" from the boiler, properly called the "pressure relief valve vent". See if this fills up when you are not looking!

Other thing IF you are competent is to open the boiler casing and locate the Auto Air Vent. Its quite likely that this maybe weeping a little. Could also be any one of several joints in the boiler which may still be under warranty.

If neither of these are causing the leak then the underfloor part must be suspect. Finding a leak in concrete is VERY difficult indeed. Best way is to look for signs of dampness where rad pipes enter concrete if the leak is near a rad connection as often is the case. An infra red camera with colour temperature contours will usually indicate where the leak is but you might need a friendly fireman to lend you one.

You MIGHT find it with an ultrasonic leak detector by listening to the heterodyned signal in the audible range but unlikely as water leaks are quite quiet.

I do have to say that statistically a leak in the concrete is common and a leak in the HW cylinder is very rare!

Tony Glazier

 

[ChrisR]

If I need to start excavating, where would I start or is this really something for the professionals?

First you have to know where the pipes run. Not too difficult to find with an infra-red thermometer (cheapest ones are now about £23).

If the pipes go up in ducting to higher floor(s) that would be a place you could possibly cut and cap them, to see if the leak is above or below.

Think of the expansion vessel as a bag of air on the system, which gets squashed when the water expands on heating. If you have a leak the air expands a bit, holding the pressure much the same as it was. If there's NO air, the pressure drops away quickly as soon as a little water gets out. Easy for a plumber to do if the fitting in the boiler is easy to get at and standard, otherwise not.
I have used a less rigid method, pumping the EV up to 3 bar and testing the pipes at 2 bar, so the air doesn't get squashed while you're testing(cold).

As Tony says air leaks are much louder. If the system were drained you could test with air and listen carefully at the rad tails, or use an ultrasonic detector.

If you find the leak isn't the cylinder, Leak Sealer, which works in the same way as the stuff for sealing car radiators, is available and would be tempting to try.

 

[stevedo]

Hi all,

thanks for the replies so far. I tried the leak sealer over the weekend without any success. If anything the rate of leakage seems to have accelerated!!!

There are definitely no leaks in and around the boiler itself. I'm coming to the conclusion that I may have to call in the professionals.

I like the idea of an infrared thermometer and may get one of these.

Steve

 

[Agile]

Just one long shot!

But firstly the IR thermometer will show where the pipes are buried but then you can often feel this yourself by hand.

Now I do have to say that I have not tried this myself but there is an electronic stud finder to find wooden studding behind plasterboard. I assume that it uses LF RF to identify the RF losses in wood compared with air.

It is JUST possible that the stud finder MIGHT be able to differentiate between wet and dry concrete but I have never tried this.

Tony Glazier