Another Boiler loosing pressure...solved?

[jimbov]

Hi I am not a plumber, so forgive me if some of my terminology is incorrect....I am hoping that one of the experts here can help me...

I Have had issues with my boiler - pressure behaving erratically. Its regularly serviced, and the problem seems to become apparrent after servicing! This winter its been a real pain. Have had a number of engineers around...told me its a leak somewhere and to monitor it...which i have

Ideal Classic ff1 200 boiler
feeds HW, 9 radiators and underfloorheating (for 1200sqft) - all zoned
megaflow system for HW storage

No apparent leak anywhere from upstairs. Not apparent in underfloor, but floor is either tiled or wood...so difficult to tell. Pipes are plastic, buried in screed.

I recently had a bathroom upstairs done, and replaced both radiators with ones that are bigger ( in terms of water volume). ...this may be relevant - see later.

Last 2 weeks have noticed the pressure drop, soon after a service. I topped the pressure whilst cool back up:
- 29th Dec - had dropped to below 1 bar. Topped back up to 1.5 bar ( whilst warm!!)
- by 2nd Jan the system had dropped again to 0.6 Bar ( I let it cool right down with everything off. Got round service engineer who checked everything and said was fine).
- checked prv - had collected app 1/6 cup of WATER ( Had placed a plastic bag to collect water since 29th ).
Boiler has since been check aagain professionally and no visible signs of leakage from heat exchanger or expansion vessel ( checked for pressure and working fine). Advised to replace PRV which I will do - however this does not explain the large loss/ fluctiations of pressure.

Also noticed the following when I fired the boiler up from cold start ( allowed 2.5 hours to cool right down to 0.6 bar before i started it again):

cold - allowed to cool right down to - 0.6 bar
started all zones and imemdiately went stright up to - 1.3 bar
after -
5 minutes running - 1.8 bar
11 minutes running - 2.2 bar
17 minutes running - 2.4 bar
then stabilised to around 2.2 bar.

That sudden rise in pressure has got me thinking that the problem is with the exv ie: that the exv ius working ok, BUT there is not anough expansion in the systm and I need a bigger vessel.The current exv has is 8L.

Can anyone advise. I have had numerous people round and all anyone says is there is a leak, but no problem with boiler.
I suspect that after the service the system is primed/ pressured at 1-1.5 bar and because the system has inadequate expansion the prv has been set off ( hence the drip)...and by the time I find it has gone down the pressure has dropped and I start the whole circle of filling etc..

Another question I have is can I just leave it to run at the current pressure is all seems ok?
thanks in advance.

 

[Blackcatgas]

Yes your Idea sounds plausable and is a common problem, fit a remote vessel to the return of the boiler and then change the prv as well as when they leak they dont tend to stay sealed as they were.

 

[mfgs]

What pressure was the expansion vessel? 8ltr is probably a bit undersized. You theory seems right to me, its expanding over the 3bar mark and blowing the PRV hence the pressure drop.

 

[JimH]

"cold - allowed to cool right down to - 0.6 bar"

Why so low? Did the engineers top up the air in the E/V to 1bar +/-... if so, then a faulty/leaking E/V would explain your problems?

Sorry didn't notice that the engineers had checked the E/V...

 

[jimbov]

The engineer did not need to top up the E/V - it was fully charged to 1 bar. I saw him check it.
He did not refill the system, as he asked me to monitor how long it took to get down to zero..before refilling.

Allowing it to cool right down however, has allowed me to understand the dramatic increase in pressure when the system is switched on from cold( +2bar!!). Pressuring it to 1-1.5 bar from cold would therefore casue the Prv to activate when i switched on..right?

Trying to take any measurement of pressure when system was warm/ active was leading me to believe that I actually was loosing pressure ie: a slow leak. I now believe (and will continue to monitor to check) that the water / pressure had already been discharged to accomdate for the exapansion when switched on, and what I was just seeing/ interpretingwas the low point(s) in pressure as the system naturally cooled down.

Expansion vessel is 8 ltrs

 

[alspeed]

Agree that expansion is a bit undersized, however i would check the braided pipe that joins the boiler to the expansion, they can get blocked, so even though the EV is charged it's not actually doing anything. Easiest fix would be to tee an external 12 or 18 litre in to the system.
Failing that you might have a tiny leak somewhere hidden.

Al

 

[Mick Helpful]

If its not the EV check the rad valves for slight leaks by tying a strip of toilet roll round the valve just below the wheel head spindle. If ithe paper get damp it'll show up in the state of the paper. If they're the packed type renew the packing with wool & silicone grease alternatively change the o-ring or the valve.

 

[jimbov]

OK ...thanks you everybody for your advice.

Had a new 18L expansion vessel fitted today, and replaced the PRV..... All unusual pressure problems in the system have now gone!

Anyone that is loosing pressure, and cant find a leak...may find this useful.....

 

[GrahamM]

Thanks for taking time to update us. It could help someone else out.
Glad you got it sorted.

 

[jimbov]

Now intermitant gurgling/ whooshing noises - Grrrrrrr!

Ok so all my pressure issues are resolved. previously while the system had been let to run down to work, obvioulsy alot of air entered the system. The expansion valve was put it and re pressurised. Engineer told me that the air would work itself out of the auto vents. I have tried to bleed radiators, but their defintely is no air trapped in raiators.

Its been running for 3 days and when the heating comes on ( after its colled down) I occasionally get a very loud gurgling sound from the direction of header / megaflow tank ( where the actuator motorised valves that seperate HW, DCH, UCW) - like water falling in the pipes....its driving me crazy!! I have an autovent placed in the same location, plus one near the boiler. 2 pumps - one downstairs for Underfloor, and one Near boiler.

Is it trapped air? Is it the pumps? any ideas? Noise seems to come from the same place everytime.....

 

[stevetheplumber]

If your vessel was under sized it would have shown at the prv your original post said you couldnt find a leak?

 

[jimbov]

Pressure issue is solved. It was undersized ev. trying to resolve new issue as per last post... thanks