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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> BAXI 105e pressure relief valve problem https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1486136491 Message started by molegrip on Feb 3^rd, 2017, 3:41pm

Title: BAXI 105e pressure relief valve problem
Post by molegrip on Feb 3^rd, 2017, 3:41pm

Hi. Have just fitted a brand new pressure relief valve to a Baxi 105e combi, one of a list of repairs it needs to stop erratic pressure. Boiler fires up fine and no leaking at first, but when it reaches full temperature (all LEDs lit) the prv starts venting hot water to the outlet pipe. At that time the pressure gauge is showing a tad under 2 bar. Is this indicating a rubbish (non-baxi) prv ?

Title: Re: BAXI 105e pressure relief valve problem
Post by CWatters on Feb 3^rd, 2017, 7:21pm

I'm not trade but...

Have you checked the expansion vessel? If that's faulty the pressure will rise too much when the system heats up causing the PRV to open. PRV can be a bit temperamental in that once they open they seem to become less reliable/accurate.

If the expansion vessel is ok then.. Have you added extra rads to the system recently? eg could the expansion vessel be too small for the enlarged system?

Related thread..
http://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1184186189

Title: Re: BAXI 105e pressure relief valve problem
Post by CWatters on Feb 3^rd, 2017, 7:25pm

PS: If the expansion vessel is faulty/too small then it's possible to add another one to the system rather than replace the one you have. Sometimes that's easier and may avoid you having to work on the boiler if that's where yours is.

Title: Re: BAXI 105e pressure relief valve problem
Post by molegrip on Feb 5^th, 2017, 7:46pm

Many thanks for that. Yes, a faulty expansion vessel was at the back of my mind when i posted the query. I've only just inherited the system via a house move, so just listing the faults with the 105e Baxi, which although probably ten years old does still do its job but in a messy way! Leaks from too many junctions etc, and leaking out of the hot water diaphragm housing pin hole which i know is a common problem. Pity the expansion unit is a boiler-off the frame job. Haven't added any extra rads and i don't think there are too many on the system. The boiler is maintaining pressure even though the prv lets by at hotter temps, because a previous fixer has placed a permanent flexible filling-loop bewteen the cold water supply and the flow (out) side of the central heating circuit - which is as far as i know on the wrong side ! (And shouldn't be left connected anyway). So it's working in its own eccentric way. If i could ask a supplementary - one of the list of jobs is to fix up that leaking hot water diverter valve diaphragm, and i've acquired a new one. According to bits i've read, including the Baxi service manual, to get the unit dry before opening up, one just shuts the cold water-in isolation valve, and opens any hot water tap in the house until it stops running - no need to drain down the boiler. But when i tried that, the hot water wouldn't run at all - only running from the kitchen hot water tap when i turned the isolation cold water-in back On. I was stumped by this, and my only guess at a reason is a massively furred-up automatic air-vent right in front of me which is another job on the list. If that is totally blocked could that be stopping the flow from the hot water side of the boiler to the hot taps ? :-/

Title: Re: BAXI 105e pressure relief valve problem
Post by Headrush on Feb 10^th, 2017, 9:45pm

The auto air vent is for CH only. Your DHW wont flow because it's air locked. Undo a DHW connection somewhere high in the boiler with the sink tap open and it will start to drain. Don't forget to drain the other hot taps in the house first to be on the safe side..