Baxi 105e over pressure

[Plipplop]

Hope someone can advise as to my next step. The initial problem was the boiler would go over pressure and blow off, hence resulting in the pressure showing <0. Called heating engineer who diagnosed a pressure release valve problem(prv) so replaced that, again, it went over pressure next statement is you need a new boiler the expansion vessel is gone. OK I accept this could be the problem but obviously wanted to be certain before I take that path as the kitchen would have to be dismantled to carry out any replacement. Asked another engineer to carry out some tests and perhaps reaffirm the initial analysis. Well he proceeded to say we should check the expansion vessel and recharge as first action, he proceeded to turn off the flow and return then drain the boiler, checked expansion vessel and recharged it to 1bar, asked to leave that way for an extended period, which we did the level on the pressure indicated on the pressure gauge dropped slightly after a period of some twenty hours. Turned on hot water after this period worked fine boiler went up to 60 degree etc. no problem, then tried the central heating having turned on the flow and return the system lasted much longer but again went over pressure and blew off. My main question is do I have to conclude that it is time to change the boiler, or should I try drawing down off a rad not being used heavily to perhaps utilise as an expansion vessel as someone suggested to again try and prove this issue. Any help on this would be sincerely appreciated

 

[ShaunCorbs]

You can get an external expansion vessel fitted aslong as it’s on the main pipework this can be anywhere

 

[John.g]

Hope someone can advise as to my next step. The initial problem was the boiler would go over pressure and blow off, hence resulting in the pressure showing <0. Called heating engineer who diagnosed a pressure release valve problem(prv) so replaced that, again, it went over pressure next statement is you need a new boiler the expansion vessel is gone. OK I accept this could be the problem but obviously wanted to be certain before I take that path as the kitchen would have to be dismantled to carry out any replacement. Asked another engineer to carry out some tests and perhaps reaffirm the initial analysis. Well he proceeded to say we should check the expansion vessel and recharge as first action, he proceeded to turn off the flow and return then drain the boiler, checked expansion vessel and recharged it to 1bar, asked to leave that way for an extended period, which we did the level on the pressure indicated on the pressure gauge dropped slightly after a period of some twenty hours. Turned on hot water after this period worked fine boiler went up to 60 degree etc. no problem, then tried the central heating having turned on the flow and return the system lasted much longer but again went over pressure and blew off. My main question is do I have to conclude that it is time to change the boiler, or should I try drawing down off a rad not being used heavily to perhaps utilise as an expansion vessel as someone suggested to again try and prove this issue. Any help on this would be sincerely appreciated

You say the EV was charged to 1 bar, do you mean by this that after draining the boiler that the air end was charged to 1 bar? and that the (water side) filling pressure was also 1 bar. It makes a huge difference if the (pre) charge pressure isn't done properly.

If you had a 100 litre system and a very modest 8 litre EV. the following pressures would result.
Precharge/filling/final (Bar)
1/1/1.59
1/1.5/2.5
0/1/2.7
2/1/2.9
Obviously installing a external EV will reduce all these numbers but even a 8 or 10 litre EV should be OK for up to ~ 10 rads if the EV is charged properly.

How many rads have you installed?.

 

[Plipplop]

John,
There are 6 rads which has been the setup since day one, the engineer charged the ev to 1 bar which showed on the pressure gauge about 1.25bar I seem to recall. If you need anymore info please ask and I will attempt to obtain. But thank you very much for your prompt reply and assistance it’s really appreciated

 

[ShaunCorbs]

There shouldn’t of been any pressure in the system when he recharged the vessel

 

[John.g]

Don't know what capacity EV is installed but even the smallest at 6 litre should have no problem what so ever in dealing with 6 rads.
You say the pressure gauge showed 1.25 bar but it should show zero while pre charging the EV, the pre charge pressure is pumped/measured at the air end (schrader valve) with no pressure at the water side, the filling pressure (water side) is/should then be increased to 1.25/1.5 bar.
The only way I can see the EV (ruling out any other problem like a leaking heat exchanger) causing excessive pressure is that the pre charge pressure hasn't been checked and is actually ~ 2bar or more.

 

[Plipplop]

John/Shaun,
I will check that I haven’t given you duff information, I saw him turn off the flow and return then drain the boiler, then recharge the EV via the Schroeder valve. If the pressure did rise when he had drained the boiler and recharged the EV what could of caused that. I will try and get hold of the engineer later but I may have to wait until tomorrow. Thanks in advance

 

[ShaunCorbs]

No drain open / water still in the boiler

 

[John.g]

When the boiler is cold what is the pressure?

 

[Plipplop]

Shaun,
I definitely saw the pipe attached to the what I presume was the drain outlet inside the boiler and a tap turned and water expelled into a bucket until it stopped, then I presume the tap was set off. john, pressure when cold is just over 1.1 bar, hope this helps

 

[John.g]

And the pressure with rads/system fully hot? Have you a combi or a unvented cylinder.

 

[ShaunCorbs]

Should of left that open when he re charged as probably the vessel was full of water so no where to go if it wasn’t open

 

[Plipplop]

John, it’s a combi boiler Baxi 105e, Shaun, I will check all of that when I get hold of the chap, don’t want to confuse you further

 

[Plipplop]

John, will check pressure when fully hot but last time it went over 3 bar and blew off, but will check that later and report back

 

[John.g]

No, that's good enough, the only other reason I can think of is that the EV diaphragm is stuck to the sides of the vessel and not moving at all.

The other most unlikely problem is that the mains water is pressurizing the system through a leaking Hx but in that event the pressure should keep rising with the boiler off overnight or whatever.

 

[John.g]

And the most obvious question of all, is the filling valve(s) closed or is it a auto fill type with a PRV (pressure reducing valve).

 

[Plipplop]

John with boiler off it did not rise overnight which I checked last night in case there was something leaking or whatever. Could please explain what filling valve is, do you mean filling loop attachment which have with a hand operated tap

 

[John.g]

That's it, and should have a flexible hose to enable disconnect but if shut off valves at either end then most unlikely to be passing.

 

[John.g]

Actually you can solve part of this mystery yourself, with system cold and pressure at 1.25 bar, just use the filling valve(s) to increase the pressure to 2.5bar. If the system has been precharged to 1.25bar then it will take 2.86 litres to increase the pressure to 2.5 bar if a 8 litre EV & 2.14 litres if a 6 Litre EV. Just bleed off from a rad or whatever and measure this amount in reducing the pressure back down to 1.25 bar.
You can do this test up to a starting pressure of 1.5bar.
If the EV diaphragm is "stuck" then the pressure will rise almost instantly on starting to top up.

 

[Plipplop]

John, thanks so much for that, cos this is what I have been looking for from those that have viewed the problem, this is great. Tomorrow I will do this and report back thanks so much for all your help

 

[Plipplop]

John, have been tied up all day so haven’t had chance to try your advice, as soon as I do I will report back, thanks again

 

[Deleted member 123817]

John, have been tied up all day so haven’t had chance to try your advice, as soon as I do I will report back, thanks again

Any update?