Why does the pressure in my combi rise by over 1 bar now I have a new pressure vessel

[honestinjun]

I have a Vaillant TurboMax plus 837E combi boiler attached to an old single pipe (cast) system with 10 radiators and a significant volume of water within the pipes alone.

I recently found the pressure vessel was leaking and was incapable of absorbing the pressure rise when the water temperature rose above about 60 degrees.

I replaced the PV with a new identical 10 litre tank from Vaillant which was fitted reasonably easily and pumped to 1 Bar.

On filling the system everything appears to work ok however when the system was running hot with the old PV (while it was still working ok), the pressure rose from 1.5 Bar to about 1.9 Bar. With the new PV fitted, the pressure rises from 1.5 Bar to 2.5 Bar.

Everything seems ok but with an old single (cast) pipe system, I am concerned that running at 2.5 Bar will put old dodgy joints under too much pressure and am also puzzled as to why there should be such a rise in pressure if the faulty PV was the only problem and this is now fixed.

Any suggestions as to why the system (configuration is unchanged) should now register an expansion of 1 Bar when it used to only increase by 0.4 Bar and given that it seems stable, is it ok to keep it running in the red at 2.5 Bar (risk of leaks aside)?

Advice much appreciated.

 

[Toddyplumb]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

What was the exp vessel charge pressure ?

 

[rsr]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

A couple of points for you to mull over:
1. expansion vessel charge pressure needs to be as stated in manuf's inst'ns and set before installing in system
2. next factor is the volume of water in the system which will dictate exp. vessel size; again check with manuf.
Over to you

Cheers
RSR

 

[fagsanbooz]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

yes, rsr is right.
Probably volume in system is too much for capacity of expansion vessel and not only check 'charge pressure' but also if you have a lot of 'head pressure' on the vessel (radiators in a tall building, with boiler at base) that can also affect the vessel and you may need to get one with a higher pressure setting (1.5bar)

 

[honestinjun]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

System was installed by an engineer who was pretty on the ball and model and PV selected to balance with system. On basis everything worked ok with increase in pressure limited to circa 0.4 Bar I have no reason to doubt the design was correct.

Something then went wrong after years of successful operation and pressure started going through roof. In checking PV, it was leaking water and diaphragm appears to have become damaged.

Issue is that after draining system and fitting new, identical PV, pumped up to the appropriate 1 Bar of pressure per the manufacturers guidelines, the pressure still appears to be rising more than is comfortable i.e. by at least 1 Bar.

Everything working ok now but I am suspicious that a brand new PV is now masking an underlying problem and I expected that putting an identical PV into the system with the correct charge would have resulted in a system that exhibited the same expansion as before i.e. going from 1.5 Bar to circa 1.8 Bar at 70 degrees. It now goes up to 2.5 Bar and while this is stable, I am concerned at running contantly in the "red" on the pressure gauge (which kicks in at 2 Bar) and also of putting an old system under such pressure and also that I have simply masked a different problem altogether.

 

[Toddyplumb]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

Your volume has not changed . Your Temperature has not changed . Its got to be the initial charge pressure is slightly different .
I would not be overly concerned, just keep an eye on it
Your filling loop is closed isnt it ??

 

[honestinjun]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

Yes and thanks for the reassurance - I can't think of anything else and hope it simply reflects that the initial installation was made with the PV slightly overcharged.

 

[cjg]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

Q,
what about fitting another PV on the system to allow for any extra expansion,

 

[GrahamM]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

System was installed by an engineer who was pretty on the ball and model and PV selected to balance with system. On basis everything worked ok with increase in pressure limited to circa 0.4 Bar I have no reason to doubt the design was correct.

Something then went wrong after years of successful operation and pressure started going through roof. In checking PV, it was leaking water and diaphragm appears to have become damaged.

Issue is that after draining system and fitting new, identical PV, pumped up to the appropriate 1 Bar of pressure per the manufacturers guidelines, the pressure still appears to be rising more than is comfortable i.e. by at least 1 Bar.

Everything working ok now but I am suspicious that a brand new PV is now masking an underlying problem and I expected that putting an identical PV into the system with the correct charge would have resulted in a system that exhibited the same expansion as before i.e. going from 1.5 Bar to circa 1.8 Bar at 70 degrees. It now goes up to 2.5 Bar and while this is stable, I am concerned at running contantly in the "red" on the pressure gauge (which kicks in at 2 Bar) and also of putting an old system under such pressure and also that I have simply masked a different problem altogether.

Dont mean to split hairs, but the MI's I have state a vessel pressure of 0.75 bar not 1.0 bar. Dont think will make a great deal of difference, but if you have pressure gauge you could try letting little bit out.
In my experience your average system pressure usually rises around the 0.5 bar or so in operation, which is what you had previous. Find it strange why it is now increasing 1.0 bar. Is your system fully blead and all rads heating properly?
As Toddy said, keep an eye on it for few days. If everything operating then would let it go, but if pressure creeps above the 2.5 bar then need go back to the drawing board.

 

[coley]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

When you say you pumped it up to 1 bar. Dont u mean you released the gas down to 1 bar they always come pre-charged. Are you taking the reading from the boiler or from a gauge on the system. If you have the make and model it might help.

Also try Isolating the pv from the system and see what the pressure rise is then
Regards
Coley

 

[kay-jay]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

the pressure increase you state for the previous exp vessel when it was working.................
well was it? could it not be that it had been developing a slow leak over a long period of time? therefore leading you to believe that the system should normally increase by 0.4bar when in fact if it was completely sealed like the new one may actually have been 1 bar??

KJ

 

[Bernie2]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

Hmm!

I would tend to try and sort it out as 2.5 bar is very close to the boiler PRV's usually set blow off pressure.

 

[honestinjun]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

Thanks to everyone for their input. To answer some questions, make and model are on the original post and to be precise I set the PV to 0.8 Bar which was in line with the original installers guide (no data came with the replacement PV) and was only about 0.5 Bar above the level it was pre charged to.

My central heating system reminds me of the one in my original primary school (1960's) with lovely looking but notoriously inefficient and temperamental 2 column cast iron radiators. Removing all of the air from the system after working on it takes months of dedication, so while I can say that I have bled the system several times now since replacing the PV, it would be reckless for me to claim this could not still be a factor.

I am going to follow the advice to see how it settles while continuing to bleed the radiators on a regular basis and will come back to this post in a months time and let you know where this gets me to.

Cheers.

 

[kay-jay]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

if air in the system is a problem look at spirotech combination valves wich remove both magnetite and air, or you can just get the air release valve. i saw one in action and it was better than any other standard heating system air release valve

 

[Billy Bob Bob]

Re: Why does the pressure in my combi rise by over 1 bar now I have a new pressure ve

what about checking the basics? your filling loop could be knackered