Ongoing pressure loss - time to dig up the floors?

[JJ15]

I've posted a couple of time on here and the responses have been really useful. However, I'm still having problems......

The guy who rents a room off me called me whilst I was away saying that my 13yr old Saunier Duval Boiler was making a horrendous noise. He'd also been away so I'm not sure how long this had been going on for. When I got back I called BG. They came and said that the pump was knackered, pressure was at zero and that it would be cheaper in the long run to get a new boiler fitted. When they re-pressurised, the pump was still not working properly.

I took their advice and contacted a local firm. I had a Biasi Riva Compact HE fitted last week. It was fitted by a Corgi engineer and I received a benchmark certificate etc. Everything worked fine for the first day or so. After I had managed to warm my flat up, I turned off the DCH and switched to DHW. I noticed that after my rads had cooled, the pressure started to drop. It pretty soon dropped to zero. I re-pressurised the system, but the same thing kept happening.

There were no apparent leaks from the boiler or any of the rads. There was also no discharge from the blow-off pipe. The original installers came back today to take a look at it. They confirmed that there was no leaking from the boiler. These also bled all the radiators (except for the one in the bathroom as the bleeding valve had snapped off). This radiator was half full of air. However, they isolated this radiator and re-pressurised the system. Again, there was no pressure loss when switched to DCH. Pressure loss only occurs about half an hour after I've switched on to DHW.

The engineer therefore concluding that I had a leak in the pipework. He is coming back on Saturday to take a look, although I suspect that repairing leaking pipes goes beyond his original installation remit. However, he is being very helpful.

The problem that I have is that I live in a ground floor. All floors are concrete.

I therefore assume that the majority of the piping is under the concrete. There are no obvious signs of dampness in any of the rooms that are carpeted. However, I pulled up the lino in the bathroom and the concrete here is pretty damp. This also contains the "problem" radiator. However, I'm not sure whether this is due to normal bathroom use or a leaking pipe.

I obviously want to be pretty sure that the problem is a leaking pipe before I start digging up my floors.

Any observations/suggestions gratefully received. I live in the North London area so if anyone knows of someone decent who could give a second opinion, I'd be very grateful.

Thanks

 

[sam8364]

If you have an old house (i.e pre WW1) that did not originally have concrete floors but which has had them later you may often find damp patches coming through the concrete.

Just a thought before digging up a concrete floor, completely knackering any dpm only to find there is no pipe there anyway!

 

[kevplumb]

put the heating on and feel for the warm bits

 

[JJ15]

Thanks. My flat is an old converted shop. Probably built circa 1890 and converted in 1990.

 

[Onetap]

put the heating on and feel for the warm bits

Bathoom floor covering is vinyl? Heating on, clean floor with mop and leave wet. The area above the pipes will dry quickly, leaving lines on the wet floor. The area above a leak will dry quickest, leaving a circle above the leak.

However, what the OP said was;

>Again, there was no pressure loss when switched to DCH. Pressure loss
> only occurs about half an hour after I've switched on to DHW.

This suggests there is no leak from the central heating pipes & radiators, but that the leak is from the circuit within the boiler that serves the DHW plate heat exchanger. Maybe a preforated heat exchanger, so the leak is from the boiler to the DHW?

There are usually F&R isolating valves on the boiler which would allow you to isolate (and eliminate) the central heating circuit as the source of the leak.

 

[Slugbabydotcom]

Maybe a preforated heat exchanger, so the leak is from the boiler to the DHW?

If that was the case case it would leak the other way into the primary circuit after drawing off water and fill your heating system up to mains pressure.

Is this what is happening?

 

[Onetap]

I'd assumed this was a combi boiler, hence my mention of the heat exchanger, but I see the Biasi Riva Compact HE is available as combi or system boilers. I don't think the OP has mentioned which type this is. Or did I miss something?

Is there a hot water storage cylinder, Mr. OP?

Agile Tony is in N London, I believe and seems a competent chap from his posts on here (except where he disagrees with me, of course ).

Maybe a preforated heat exchanger, so the leak is from the boiler to the DHW?

If that was the case case it would leak the other way into the primary circuit after drawing off water and fill your heating system up to mains pressure.

Is this what is happening?

Usually ( if it is a combi) unless there a pressure reducing valve or low mains pressure, in which case the boiler pressure might exceed the mains pressure when the system is hot and then leak from boiler into DHW.

 

[JJ15]

Thanks for your replies.

It is a combi boiler. When you say hot water storage cylinder, do you mean an immersion tank? (sorry If I'm asking a stupid question). If so, then no, I don't have one.

Like I say, when the DCH is on, pressure remains constant. Had the heating on for 12 hrs yesterday to test it, came home and it was still on 1.5. Turned to DHW and after an hour or so, down to zero.

You'll have to be patient with me, but can I ask a couple of stupid questions?

1. If I have a leak in a pipe, wouldn't it also leak when using DCH and not just DHW?

2. Can I determine whether I have a leak by turning off all my water appliances and checking my meter to see if it's still spinning?

I guess what I want to try and determine is whether (a) there was a problem with the installation (which is under warranty) (b) there is a problem with the boiler (which is under warranty) or (c) whether I have a leak. If it is a leak, then I'm slightly annoyed with the original BG man who took about a millisecond to look at my old boiler and said, "the pumps knackered" you'll need a new boiler. If I was losing pressure before the installation of my new boiler, I assume that this may have led to the pump running itself dry over xmas? Sorry for all the questions.

As an aside, I have found this much more user friendly that the manual! It has also armed with some basic knowledge so that I can at least understand bits of what the engineer is saying! So thanks spending time replying.

 

[Slugbabydotcom]

Turned to DHW and after an hour or so, down to zero.

So you ran your HW for over an hour ? You must have a big bath!
This is the time to check your PRV. Is it possible that the pipe does not run through the wall as you expect and may be broken or disjointed?

1. You would expect so, yes, but there are sometimes a few anomalies in the world of heating and this could be one of them.

2. Wasting your time with that one as you effctively create a leak by turning the hot tap on to make the thing leak

Monitor more closely what happens to the pressure when you are drawing off HW.

There are only so many places that this water could be going to.

If it was the boiler then that would be an obvious leak in front of you

If it was the PRV it would let water through it at some stage.

The only major thing left is the sytem.

After that we start grasping straws

The SHE could be letting some water out into the hot water side with a bit of debris acting as a one way valve.

Your filling loop non return valve could be the wrong way round AND the valve doesnt shut off properly AND you mains water is only at 1.5 bar

The main heat exchanger could have a leak that when the higher flame required for DHW a tiny crack opens up in the HE and this lands in such a way that it evaporates into steam before you notice a leak.

How rare is any of that? yet it is feasible

We have now travelled from grasping at straws into the twighlight zone where aliens and poultergeists etc could be responsible after everything that has now been suggested.

 

[Onetap]

Thanks for your replies.

When you say hot water storage cylinder, do you mean an immersion tank? (sorry If I'm asking a stupid question). If so, then no, I don't have one.

Yes

I would suggest that, with the boiler and heating system cold, you turn off the heating and shut the two isolating valves for the heating flow and return on the bottom of the boiler.

Then run the hot water system normally and see if the pressure drops.

If it does, then you have established that the leak is from the DHW primary circuit within the boiler and it is a warranty problem for the installation contractors to sort out. This is assuming that neither of the two isolating valves are letting by and allowing water to leak into the heating system. If they do leak, then that is also a warranty problem for the installers.

 

[JJ15]

Thanks, when I say turn to DHW, I mean change the setting on the boiler from DCH to DHW. Pressure drops regardless of whether or not I'm drawing hot water. Will try both your suggestions. Thanks

 

[Onetap]

PS

Are you sure it's not simply a leak from the bathroom radiator air vent that they've mangled up? There's a leak in the immediate vicinity and that radiator also fills up with air.

Although it has ben isolated, the rad valves don't always shut off completely; some earlier TRVs can't be shut off without removing the actuator head and fitting a knob.

 

[JJ15]

Thanks Onetap.

I called Biasi this morning. They suggested (as did you) that I shut off the two isolating valves for the heating flow and return on the bottom of the boiler. I was told that these should have little plastic caps on them and it is just a matter of tuning them off. I had a look at my boiler this morning (I'm now at work) and I have a yellow and blue cap, but they do not seem to correspond to the heating flow and return pipes as shown in the manual. Now more confused than ever!

 

[JJ15]

Hi, have done what you suggested. I pressurised up to 1.5 and turned off both the heating flow and return valves. The boiler hasn't lost any pressure. Presumably this means that the problem isn't the boiler but the heating system?
Thanks

 

[Agile]

This is all falling into place now!

When you open the heating valves you will presumably find the pressure reduces to show that its the system leaking.

Follow the procedure I explained to you to emphasise the leakage rate to aid detection.

Tony