Unvented system; loss of pressure but no leak All aspects of plumbing questions and answers, help, tips and information

[Ravster]

I have an unvented sytem (Megaflow). Few months back we discovered that the system kept on losing pressure (and hence the boiler shutting off). The loss of pressure is quite rapid - within 2/3 hours!

I was informed that the loss in pressure was due to a leak in the ground floor as there was no sign of leaks upstairs. Most of my ground floor is tiled so extremely difficult to locate the leak. Over the last 4months I have tried various means of locating the leak/leaks but to no avail. Finally I hired the services of a firm specialising in leak detection they use infra red cameras, sonar, etc). They have reported that they are 99% sure that there are no leaks. They recommend me to get someone to have a look at the Megflow system as they suspect that is where the pressure is being lost.

Before I go and do so, I should be grateful for your views and thoughts as to what are the probable cause of pressure being lost in the system (i.e not due to a leak).

[AdamsHeating]

It could be a leak on the expansion vessel? check this in line with your manufacturers instructions. if you locate the valve on the vessel and push it in (only for a second mind you) and you get a wet finger it is leaking and will cause pressure to drop, and will need replacing. if no water then it is not that.

It could be a leak inside the boiler, check around for signs of scale formation or corrosion.

If it is a system leak you can locate it as follows:

Shut all isolation valves on the boiler (underneath and a quarter turn). If the pressure stops falling with the boiler isolated then the leak is on the system (rads, pipe, etc). If the pressure continues to fall then the pressure loss is due to the appliance (refer above).

One other thing is that the Safety Valve could be passing, do you have one and is it leaking outside?

regards,

AH

[Ravster]

"AdamsHeating"

Thanks for the detailed response. I will perform the checks this evening!

I was recommended to build the pressure up to 1.5 bars without switching on the boiler and check how long the pressure is maintained. I discovered that building up to 1.0 bar was quickly but it was struggling to go beyond 1 bar. Shortly after I turned off the filler, the pressure started to fall!

[AdamsHeating]

So it is definitely leaking somewhere then, just a case of tracing it.

If the boiler is attached to a cylinder, sometimes the coils inside the cylinder wear away, not sure if this will be the eventual answer but just thought i;d mention it.

You will probably have to get a specialist unvented gas man in to check it over for you if you can't locate the leak.

regards,

AH