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Jerry
Jerry, Plumber
Category: Plumbing
Satisfied Customers: 760
Experience:  Residential journeyman plumber, over 20 years experience.
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I have a Baxi Instant 105E, and the pressure drops to 0 when

Customer Question

I have a Baxi Instant 105E, and the pressure drops to 0 when it is not running. The top two radiators empty, and I have to open the FW valve to re-pressurise the system at least twice a day. Should the FW valve be constantly open to keep the pressure up or is there a vent leak that I don't know about. There are no water patches anywhere or leaks on the system that I can find. Many thanks.
Submitted: 3 years ago.
Category: Plumbing
Expert:  Andrew Smith replied 3 years ago.
Can you tell me if the 15mm copper pipe that exits the wall about 3ft below the flue is dripping when you top the system back up?
Customer: replied 3 years ago.


There's no condensation or water leakage anywhere. The boiler is located in the kitchen over the counter and there has never been an accumulation or puddle of water at any time.

Expert:  Andrew Smith replied 3 years ago.
Outside, under the flue?
Customer: replied 3 years ago.


Nothing there either, dry and no indication of there being any form of leak.

Expert:  Andrew Smith replied 3 years ago.
Ok, when you refill the system put a plastic bag over the pipe and leave fr 24 hours and let me know
Customer: replied 3 years ago.


For your information, I refilled the system this morning at 0830, and ran the system to reheat the water and radiators, which has now depressurised to 0 bar. There is no leak of water or condensation anywhere in the house, nor outside under the flue.


 


Should the FW valve be open fully and constantly, or is it left shut?

Expert:  Andrew Smith replied 3 years ago.
Can you locate the 15mm copper PRV discharge outside?

One way to know whether it is boiler or system is to turn the central heating isolation valves off under the boiler and refill the system - let me know what happens?

The filling valve should be used to top up the boiler and then turned off again.
Customer: replied 3 years ago.


I've had a look and there is no PRV discharge pipe, and is only the flue outside. Whether this would be in the fabric on the wall and venting underground, I don't know as this is a rental property.


 


I shut the system and the valves, refilled the boiler, vented and re-flashed up the boiler. The pressure dropped to 1 bar, so I repeated to 2 bar and re-flashed up the boiler. The pressure has now climbed to 3.5 bar, so I've returned the system to timer and will see if it drops.

Expert:  Andrew Smith replied 3 years ago.
Ok, let me know, but there has to be a PRV discharge somewhere. Perhaps at ground level?

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