Boiler Pressure Loss

[CLairehead]

I've been out to a customer today with my mentor to have a look at a combi losing pressure problem.

The original system was a open vent system and now its gone to a sealed system. The plumber that fitted the new boiler has looped the pipework in the airing cupboard negating the previous S Plan system and taking out the HW cylinder.

In the process of refitting there is a very very small drip/weep coming from one of the solder joints, I could never imagine a solder joint to drip that small amount, maybe 50ml in a day. However the customer is reporting a pressure drop from 1.0bar to 0.5bar in the space of 2 days. I did a rough calc on the volume of water in the system and I think its about 120litres.

Can that small amount of water loss cause such a big pressure drop?

Also I don't know if its related but the customer is reporting lots of air in the upstairs radiators. My thought was if the pressure in the system is higher than 0 bar gauge, how can air enter the system?

Thanks in Advance

Claire

 

[muggles]

It won't take a huge amount of water to cause a pressure drop, no. If there are weeps on soldered joints then it's also possible that upstream of the pump similar weeps are allowing air to be drawn in

 

[plummerman]

In short Yeah.... System isnt airtight is it. If water can come out air can certaintly be pulled in as the system is in operation. And you dont know if theres other leaks on system as well.

Was system pressure tested before changing to fully sealed? Is all pipework exposed? Or any under downstairs flooring which wouldnt show a leak... Custard would never know there was a leak there as header would just keep filling to compensate

Just cause you cant see water damage doesnt mean there isn't a leak.. Mirco leaks for instance. had one recently. Installer adamant leak was on boiler. 'all my pipework exposed, apart from upstairs under floor, got no stains or damp patches on ceiling' Guess where his leak was

 

[commercialman]

Also I don't know if its related but the customer is reporting lots of air in the upstairs radiators. My thought was if the pressure in the system is higher than 0 bar gauge, how can air enter the system?

Many issues can contribute to air ingress , one reason would be loss of system pressure (as in your case) , this can cause suction side of circulator head to fall below system pressure (sub atmospheric) , this drop in system pressure will release any air that was previously absorbed in system water , add this to micro leaks at stuffing boxes/glands & you will see it won't take long for air to collect in high points of system.

If system pressure was filled below expansion vessel charge pressure it won't take much water loss to show zero on gauge , this is sometimes the case when vessels are pre-charged to 1.5 bar & system pressure set to 1 bar.

 

[CLairehead]

System was not pressure tested before going to the sealed system. Its about 10 years old but 95% copper

I shall sort this leak out today and see how it goes, I had never really thought about the pre-charge pressure, so I will check that too.

I was going to leave the boiler pressured at 2bar and shut the flow and return valves to see if the pressure dropped over time, this would rule out the boiler. However I tried this the other day on a Viessmann 300 and the pressure dropped, I eventually found the leak but it would appear the valves were passing ever so slightly, hence connecting the flow and return and then pressuring might be the best course of action!

Thanks

Claire

 

[algas]

Also Claire if the system has been repeatedly topped up you will most likely have hydrogen gas build up in the rads