GLoworm 30CCI low pressure and unable to fill

12 Jan 2006
Reaction score
United Kingdom
Gloworm 30ci suffers low pressure red light comes on in the morning. Pressure stuck on 0.5 bar. No leaks noticable on the system. Unable to fill the system and pressure is stuck on 0.5 bar. When filling up plenty of water comes down the boiler out of brass valve that sits at the end of copper tube from internal filling loop. It appears no water gets in the system. FIlling loop has plastic blue cap (valve) but the leak is on the other side of copper tube out of brass valve.

I suspect blockage or fault on Reduced Pressure Zone Valve. As I try to fill boiler there is leak on brass part of this valve. I had to use screwdriver with cloth over the tip to close RPZ drain off hole to fill boiler in the past but now can't do this either. It looks like the filling RPZV valve is blocked? is this possible?

Where can I get replacement part in NW London. I have searched net but could not find part no.

Any advice on part no, for RPZ or web site. Can this be cleaned up or repaired? I had same problem in March and have managed to fill boiler to 0.7 bar. Now can't even do this. presssure stuck on 0.5 bar if I turn boiler off/on works fine green light comes on.

Other possibility is that electronic pressure display is not reading correct pressure. and is stuck on 0.5 bar?

PRV was changed last time in March and did not fix problem. Boiler engineer has given up after 3 visits. No leaks on pipes or radiators.
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The Reduced Pressure Zone valve should only leak a little when you initial open/close the filling valve. If it leaks all the time when filling its faulty.

Your cold mains pressure needs to be somewhat higher than the required boiler system pressure - this is the big disadvantage of an RPZ valve (why most sensisble manufacturers don't fit them!). So if the street pressure is only a Bar you won't be able to presurise the boiler. (Permanent filling loops require the RPZ to comply with water regs.)

For now give the expansion vessel a dozen pumps with a cycle pump - that will often raise the system pressure to get the boiler going. Then replace the RPZ valve and the filling valve (unless its the later type). Plenty of mail order or boiler spares merchants around.

When you drop the system pressure to zero bar (to change the RPZ) check the pressure in the exp. vessel..see FAQ's for details.

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