Losing pressure, but no leak detected by gas tracer

[Sarah321]

There is a very basic test which all of them should have done to identify if the loss is from the boiler or the system.

Nothing you have said has indicated that ANY of them did it!

Tony

I am pretty positive that this has been done. I have to say that although nothing has been solved, the BG engineers have all tried really hard to get to the bottom of the problem. Also, I don't think they would have referred me on to other companies (Dynorod and Munters) unless they had exhausted every other avenue - after all, as I am insured with them, they have to pay for them to come out to me.

Basically, BG are saying that there's a leak under the floor, and Munters (Polygon) are saying that it's not showing up on the gas tracer as a leak, so it must be a fault with the boiler. I, in the meantime, am left between a rock and a hard place.

 

[Sarah321]

Cylinder still gets my vote. Assuming the guys with the fancy kit know how to use it, and you really don't have a leak under the floor.

If you continue to add fresh water you'll block the system up with sludge and corrosion, then BG will want a powerflush for £700.00 not covered by the insurance.

At the moment, the way that it's been left is that the leak detection specialists are coming back WITH BG engineers so that they can go through everything again and carry out another gas tracer test. If that doesn't work, I'm going to have to have the system re-piped as a next step - and even then, there are no guarantees that it will work. Thank you for tellling me about blocking the system - I have tried to repressurise the system as little as possible by keeping the heating off when bearable, but I must admit that I have been filling it a lot in this cold weather thinking that if I didn't have a leak, it would be fine - I had no idea I could do any other damage (aside from that which a leak may be doing). Thank you for your help.

 

[doitall]

The first thing they need to test is the cylinder.

 

[Sarah321]

The first thing they need to test is the cylinder.

Brilliant - I will ask them to do that when they come out. I will let you know what happens but it may not be for a week or so as BG are liaising with Munters so that they can come at the same time - and I have no idea when that will be. Many thanks x

 

[Agile]

Basically, BG are saying that there's a leak under the floor, and Munters (Polygon) are saying that it's not showing up on the gas tracer as a leak, so it must be a fault with the boiler. I, in the meantime, am left between a rock and a hard place.

Its very easy for them to each say that.

However, this simple test should have been done by both of them to determine if its in the boiler or system.

I am not impressed !

As for BG changing a part which did not cure the problem that smacks of desperation!

 

[mr_vampy]

I had a similar problem with my Worcester boiler in that when the central heating came home, the pressure would drop down to 0 in the red zone. The pressure was perfectly fine when I was using the hot water. Turned out that the pressure vessel needed replacing.

 

[nickso]

Do I understand correctly? A leak lasting 6 months with various contractors doing their seeming best to resolve the issue with various methods involving a concrete sealed system, and the one and only thing that seems not to have been done (isolating the boiler from the system for one day to determine the general site of the leak) is now the sole fault of BG?

An all new high in the BG bashing stakes.

 

[Agile]

Sarah, you may not know but BG now own Dynorod!

I dont know about Munters.

Tony

 

[PHILOSOPHERDAN]

Hi Sarah

I had a similar problem – it lasted about 5 years, starting with monthly topups and gradually got to the point where it needed topping up once or twice a day. The problem was that the expansion vessel was not at the correct pressure. My plumber did not identify the problem – I found it through googling. In an earlier post ‘Picasso’ and 'mr vampy' mention the expansion vessel, as it is an obvious explanation of your problem. Do you know whether it has been correctly pressurised?

As the radiator water heats up, it expands. Normally it would then flow into the ‘expansion vessel’. However if your expansion vessel is not properly pressurised (whether because it is faulty so needs replacing, or because your plumber has not pumped it up) then it is already full of water, so as the water heats it cannot go into there. Therefore it is dumped outside through the overflow valve. Then when the water cools down again, hey presto, there is less in the system, so the pressure is much lower.

Do you notice that the pressure increases when you initially turn the heating on? So it starts at 1.5bar, and then increases? And is it the case that when you only use the boiler for tap water then the pressure does not reduce (ie it only reduces when you use the heating – if there were a leak in the pipes then the pressure would reduce whether the heating were on or not)? And is it the case that when the heating turns on and the water starts warming up, then you can see dripping from the overflow pipe outside? If the answer is yes to these questions then that would indicate an issue with the expansion vessel.

I managed to repressurise the expansion vessel myself on my Vaillant boiler:
Drain the water from the boiler.
Locate pressure valve on the top of the boiler.
Attach car pump with pressure guage.
Pump up to the correct pressure (see manual or contact manufacturer).
Then refill boiler.
Mine needed a lot of pumping, and whilst I pumped, water was expelled out of the drain point of the boiler – indicative of water being pumped out of the expansion vessel. Now the pressure hardly changes when the heating turns on, and the pressure remains constant.

Obviously you can ask a plumber to do it... Perhaps you could check whether any of the plumbers who have been there have pressurised the expansion vessel – if not then I would have thought it worth a try.

If it has been pumped up, but then quickly deflates, then a replacement is needed. You can either get one for the specific boiler, or you can get a general one (its only a small metal tank) which can be fitted to pipe work anywhere on the system. Another alternative is that on the forums somewhere Tony (Agile) pointed out that you could do without fitting a replacement expansion vessel if you introduce a reasonable quantity of air into a radiator that’s little used – which would then operate as the expansion vessel – which sounds logical, and cheap …

Good luck

Best wishes

Dan

 

[picasso]

If the expansion vessel was the problem the pipe outside would have water running (especially as the amount the op has to top up the system) thats why it was discounted as the possible cause.

 

[doitall]

I think even BG would have checked the expansion vessel, although not guaranteed, when the headless chicken are at work.

"Can't see the woods for the trees" come to mind, I may be wrong, but the great big round thing staring you in the face, is the only logical answer.

If it goes on much longer, I may have to have a day out in Oxford

 

[Sarah321]

The pressure drop happened very suddenly. The heating had been fine for over 2 years, then one day, I noticed a gurgling in the rads, so bled them, repressurised and then within a 24 hour period, pressure was at zero. No visible water was coming out of the overflow pipe - or anywhere else for that matter - so I called my original plumber who did various things, including turning the red tank (don't know what this is called!!) up the right way as it had been fitted upside down. This made no difference. Leak sealant was put into the system, which had little/no effect. During the summer, I noticed that loads of water was now coming out of the overflow pipe, so I told BG and they came out and I will list below what they have done (you may need to interpret this as I am copying from their handwriting!)
01/12 Pumped up both expansion vessel, red and white. Replaced valve on white expansion vessel.
At this point, even more water started coming out the overflow, and pressure still dropping, so I called again...
08/12 Condensate checked and no signs of excessive water. Checked expansion vessel; Refitted C/H zone(?) valve due to not fitted to body properly. No change in pressure during visit (with me for 2-3 hours)
Obviously, as soon as he left (within about 30 minutes) the pressure dropped to zero. So the next day, someone else came out...
09/12 Deconnected condensate under boiler - left off. Turned off boiler
At this point I was left for 24 hours with an icecream tub under the disconnected pipe behind the boiler. After an hour, pressure was at zero, and no water in the tub. Hea came back the next day to reconnect.
At this point, I think they called in Dynorod - who came 3 times. They couldn't spot anything. So the independents were called in - Polygon. They couldn't find anything with thermal or sonar equipment. However, he did find what he considered to be an excessive amount of water coming through the condensate pipe - but this was while the heating was on (which I believe makes a difference), and it didn't dribble out, but it was expelled at about a pint or so each time. He also found, under my kitchen cabinets, a lot of condensation dripping from the pipes. He then reported back that it could be a problem with the heat exchanger and said that it needed to be checked and sent in photos of water pouring out of the condensate pipe. At which point BG came in and changed the heat exchanger. To no effect. Polygon then came back to do the gas tracer. They pressured the system to 1 bar for over an hour and no gas escaped. The only thing he did say is that this test is done when the pipes are cold, and it is within the realms of possibility that the water escapes as the copper pipes expand and contract. Over the summer when the heating was off and I only had the hot water on, I did lose pressure but it took around 3 days for it to go from 1.5bar to zero. Definitely, most water is lost as the system cools. I really hope I haven't bored you all too much!

 

[doitall]

The system should be tested at twice working pressure, 2-2.6 bar.

White vessel ?, does that mean you have an unvented cylinder with no storage tank ?

What is the make/model on the cylinder, a pic would be better.

 

[Onetap]

The first thing they need to test is the cylinder.

Wouldn't a split in the cylinder coil show up on a pressure test? Isn't it more likely that it is a leak from the main heat exchanger, but that it only leaks when the boiler is hot and everything expands?

Is there a dye available that could be added to the water to identify a leak into the condensate drain? Are there isolating valves that would allow the cylinder coil to be isolated, in order to eliminate it as the source of the leak?

The water has to be going somewhere.

A leak under the floor? Pressure tested.
Into the cylinder?
Through the boiler PRV? Checked for discharge?
Into the heat excahnger and up the flue &/or out the condensate drain.

 

[doitall]

Yes and no Onetap

They only pressure tested to 1 bar so no it wouldn't.

The bigger worry is if it's an unvented cylinder, then that will not be the problem, as the pressure within the cylinder would also increase the system pressure, (in reverse if you know what I mean)