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How to track this fault down

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Mark Grundon

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Like a lot of people here, I have a combi boiler (Glowworm 30SXi) that's losing pressure over the period of a few hours. Once the pressure is gone, the heating stops and I have to charge it up again.

I had a couple of plumbers in to replace the wifi thermostats and while they were here they charged up the pressure vessel with air but that didn't help. I will get them back in again at some point but I am wondering how best to find out where the fault is myself? I don't fancy paying them to dig up every floorboard in the house until they find a leak ;-) I'd rather narrow down the search a bit. I can't see any sign of a leak anywhere at the moment. Is there a procedure to follow that would help?

Incidentally, if the combi is heating only the hot water, it's fine and doesn't seem to lose pressure; it's only when the central heating is being used.

M
 
Once you've refilled the system and then put the boiler on, does the pressure rise gradually and stop or does it rise quickly?
 
Cbarfing the vessel is all well but what happens quite a bit is that the schraeder valve leaks air and we're back to square one. Scraeder valves are pennies in Halfords. If that is ok and pressure is still being lost you'll need to turn the boiler power off overnight and see if water is being discharged through the condensate pipe. If it is, you heat exchanger is knackered.
 
Could be a few things, top it up and run it, does the pressure rise as the system warms?

When the system is off and cold, does water drip from the prv (copper pipe outside) or less likely condense pipe if its possible to see this (white plastic pipe)
 
Hi all and sorry it's taken so long to get back on this.

When I charge up the pressure manually so that the boiler starts up the display quickly changes from showing pressure to temperature so it's very difficult to see what happens next re. pressure. The one very obvious thing is that there is a constant trickle of water coming from the outdoor overflow pipe while the pump is working. I was told to expect some water to be condensing through the overflow but this is too much to be just condensation. If it helps I can take a video and include a link.
 
If you would that would be great
 
Mate, if the vessel has been charged yiu have to check thescraeder valve on the vessel isn't leaking..(spit test). If thats ok and the vessel is charged correctly then you have a blockage in the pipe from the vessel or close after. Invariably the engineer can feel real pressure if this is the case when pumping it up. Finally there may be crud on the PRV or indeed the spring may be weak on it...replace. There's nothing else in my head...I know no more...!
 
I have a good idea what is wrong with that but it means going into the boiler so sorry cant give advice .
 
Get another GSR in,sounds like still a problem with expansion. Posts above have covered things that it's going to be. They should be able diagnose.
*were the wifi thermostat plumbers gas safe?
 
I would get the engineer back out you had last time mate. If it is a blockage the case will have to come of the boiler which you cannot do. Sometimes it is better and quicker to do this. Also when topping the pressure up keep turning the power on and off and the pressure will keep displaying.
 
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