Pressure drop on unvented system

[graymond1111]

Hi, this is my first post on this forum so apologies if terminology etc is incorrect but running out of options with this problem before escalating to insurance to trace leak. To summarise

Worcester 30 CDI Classic Boiler, Albion Ultrasteel 180L Indirect tank, Zilmet ultra pro expansion tank. Both boiler and tank connect to the same copper expansion pipe just before going outside. This has been leaking water (enough to fill up a half pint glass over night).Boiler loses pressure every couple of hours (from 1.5bar to 0). Steps taken to date (via plumbers).

1. Initial thought was boiler fault, Worcester came out and replaced pressure valve. Subsequently isolated the boiler through the two valves underneath. Pressure remained static for 24 hours. Open the pipe and pressure drops to zero. Boiler passed as working fine.

2. Appears that the water coming through expansion pipe is coming from the tank - when water is heating, it's clear that water is flowing rapidly through the tundish. I have a plumber coming out to look at the 'external' expansion tank (Zilmet) as when pressing the valve on top, no water or air comes out (not sure if this indicates a problem).

3. No apparent signs of leaking coming from pipework in ceilings or walls, radiators checked (wrapped tissue around all valves). there is some pipework going under the kitchen floor which could be an issue but i am hoping this is a last resort.

My question is, can the issue around tank and/or expansion tank leaking through tundish be connected to the boiler pressure drop or is this simply coincidental? From my simple testing, there seems to be a direct link between topping up the boiler pressure and water flowing out of the expansion pipe (not the one from the boiler has i've checked this a number of times and it is dry). Local plumbers seem to doubt it.

Any help or guidance would be appreciated.

Thanks

Gareth

 

[32 Heating]

It sounds to me that your expansion vessel is flat mate. Air should come out the valve. If it's flat the expanding water in your system has nowhere to go so the pressure builds up and the pressure relief valve dumps it. The expansion vessel should be pumped up to around 1bar. The same for the vessel inside the boiler of which I'm sure that model Worcester does have one in. The external one by your invented cylinder will be for the hot water if it's a white one.

Set your boiler pressure to 1.5bar then run your heating and see if the pressure rises up high to the 3-3.5 area

 

[simond]

If I understand correctly both the boiler system and the HW cylinder are losing water.

The Zilmet UltraPro is a potable unvented and is total crap - you'll be lucky to get 4 years out of it. Got two to do this week, coincidentally. See if you can replace it with a different make such as a Reflex (German made).

The expansion vessels in Worcesters are not Zilmet, and your test of isolating the boiler with nil pressure drop result has shown there is no boiler fault extant.

I expect the two are linked insofar as only when the boiler is working (ie: it has more than 0.5bar in the pipes) does the HW cylinder warm up, and the expansion in the HW cylinder into a non functioning Zilmet expansion vessel is causing the pressure valve to lift.

So you need a new expansion vessel for the cylinder and someone to look for a leak in the central heating system, is my reckoning.

 

[graymond1111]

Thanks both for the reply and advice. We got the external tank re-pressurised under the warranty last week but as you say, it's solved the issue of water coming out of expansion pipe but still doesn't help the heating system. Boiler pressure drops from 1.5 bar to zero in a few hours (max). I am told this is the equivalent of around a pint of water so would have hoped to have noticed this if pipes in ceiling or walls were leaking. I've even been topping up constantly to try and force more water out to see if it makes itself noticeable but nothing yet (obviously not doing much good to the boiler but need heating and water as we have young children). I've hired a local company to try and trace the leak through thermal imaging and gas detection. No idea how successful these are but it costs enough and will post back the results here. My guess is it's somewhere in the kitchen (under the tile and buried in concrete!).