biasi combi boiler m90f.28s slowly losing CH pressure...?

b33man · 25 Feb 2010

Hi all,
I have a Biasi combi boiler m90f.28s, its slowly losing CH pressure in the last few weeks. The loss in CH water is about 0.4bar per day. The external system is ok, can't find any leaks.

At first, thought it was the heat exchanger because when it had its service back in November, there was green (copper sulphate) on the fins. Its still there, but there isn't a leak, had it off all day to see.

Also in Nov, I serviced the 3 way div valve - it leaked so I dismantled it and re-greased it, it works great and no leaks.

Today, I found, after i put a bottle under the safety discharge pipe, about a cup full of water - it seems to be a leak from the pressure relief valve.
Can anybody describe how this can be fixed?
What are the short term problems with this fault?
Thanks for your help in advance

heating12 · 25 Feb 2010

could be the expansion vessel pressure needs checking ,if its wrong will disharge at 3 bar

Happyplumber · 25 Feb 2010

check in the sticky and FAQ section on how to repressurise the expansion vessel

This should sort out your problem

Agile · 26 Feb 2010

You dont have to repressurise if its working properly.

Pressurise to 1.5 Bar when cold and turn on CH.

See what pressure increase occurs when the rads are hot. It should not rise above about 1.9 Bar.

The EXV is only faulty if the pressure increases above 2 Bar in which case repressurise according to the FAQs.

Tony

b33man · 26 Feb 2010

Hi Agile,
Thanks for that, it appears to be working properly at the moment except for pushing out about 1/2 pint of fluid from the safety discharge pipe. It drops about 0.4bar so I've been refilling regularly.
But, I've just noticed that it is running hi pressure, when hot, between 3 and 4bar so I will need to repressurise.

What are the consequences of running it in this condition, for a week or so? It also started cycling through the ignition, once or twice, before running correctly.

Other than this fault, its been a damn good boiler, since 22/10/2002 (B&Q)its had a fan in 2005 and the 3w div last year. There's a slight leak on the HE, but I'll repair that in the summer I hope. I've serviced it regularly, but forgot to check the EXV pressure. Although, the max bar has never been above 2bar till a few weeks ago.
Pete

Agile · 27 Feb 2010

I have been to an annoying number of failed EXVs on early M90s.

For a week it will not make much diffference but every time you repressurise new oxygen is brought in which will rust the inside of the rads.

Tony

DeltaT · 27 Feb 2010

Check your pressure relief valve(it may be passing water) & expansion vessel pressure, when the boiler is drained. It should be about .75Bar.
If none of the above cures your problem, then you need to fit a larger expansion vessel.

b33man · 27 Feb 2010

I turned off the unit last night and this morning checked the EXV pressure. It was virtually nil, and had a bit of damp hit my hand, reckon this is condensation.

So I set about repressuirsing the EXV.
Turned off the flow/ret cocks and opened the drain next to the pump. At first nothing much came out?? Then pumping the EXV with mifootpump, an unexpected ammount of CH water came out which nearly caught me out. Must have removed >5L, anyway it took some time to pump all the water out and to get some pressure in the EXV. Finally, it started to come up and set it to 1bar (14.5psi), then rechecked it about 3 times to be sure, leaving 10min between checks to see if there were leaks.
Let water back in system, opened cocks, bled pump and set pressure to 1.3bar, run it for a bit. Then rebled all rads, pump and set pressure to 1.3bar (must check when cold again).

I've just run it to max temp (7) and get a pressure reading of 2.2bar, supposes this is ok.
Nothing comes out of the PRV now.

Agile, I can't see how the air gets in the CH water system to rust the rads if the EXV is sound?
I can see that damp air in the EXV will in time rust it and cause fault.

Agile · 27 Feb 2010

b33man said:
Agile, I can't see how the air gets in the CH water system to rust the rads if the EXV is sound?

I can see that damp air in the EXV will in time rust it and cause fault.

You cannot see but the mains water contains dissolved oxygen! Thats what the fish breathe!

The ( proper ) instructions for repressurising the EXV require all the air is released first whilst maintaining system pressure, that will eject most of any leaked water.

The pressures are not best that you have set to. Air with system open to about 13 PSI and system cold to about 1.5 Bar. Then it should not increase above about 1,8 Bar.

Tony

DeltaT · 27 Feb 2010

You cannot see but the mains water contains dissolved oxygen! Thats what the fish breathe!

The ( proper ) instructions for repressurising the EXV require all the air is released first whilst maintaining system pressure, that will eject most of any leaked water.

Thanks TT I missed that bit.
I good indication of correct sized expansion vessel; is if the pressure doesn't rise too much when the boiler is hot. It's simple, the vessel should absorb the most of the expansion.

b33man · 1 Mar 2010

...but the mains water contains dissolved oxygen! Thats what the fish breathe! ??

Just back from over the pond and it's better than ever, released a bit of pressure and now max is steady at approx 2bar. Better half reckons that DHW is better controlled.
Regarding the mains water, I don't have much in my system. Its microbore etc , my own design after I did all those U calcs way back when. This system has a low CH fluid capacity (hence, hot rads very quickly) and amazed the sign off engineer at the time I provided. When I installed the rads (all 16), etc, I filled them all with Fernox plus 5l antifreeze. Then to get up to the correct pressure I added mains fed water. When I have done any work since, I always top up with Fernox etc (thru bleed valve), consequently from 1988 I have not had a rusted radiator or seen fish in this "water". I have heard that in an enclosed pumped system the air is bled out automatically by the boiler valve so CH fluid becomes deoxygenated?
I released all the air from the EXV prior to repressure, which is stated in the relevant FAQ. Apologies to anybody who is following this and not the FAQ.
The pressure values I have used are those recommended by Biasi in my commissioning manual, and here http://www.biasi.co.uk/images/manuals/GARDA/INSTALLATION_USER/0502 EDITION.pdf I checked it. What are the reasons for your values?

Agile · 2 Mar 2010

b33man said:
I have heard that in an enclosed pumped system the air is bled out automatically by the boiler valve so CH fluid becomes deoxygenated?

The pressure values I have used are those recommended by Biasi in my commissioning manual, and here [url]http://www.biasi.co.uk/images/manuals/GARDA/INSTALLATION_USER/0502 EDITION.pdf[/url] I checked it.

What are the reasons for your values?

I wonder where you heard that! I hear a lot of rubbish at pub bars!

The AAV is designed to remove free air and this is best done at very low prerssure as part of the recommissioning after a boiler/system has been drained. On a combi alternate between heating and CH

In this case you were not asked to drain the boiler but just to release the pressure so there should have been little air.

Its best to release almost all the air as far as possible BEFORE the system is fully pressurised. Once the system is pressurised the oxygen dissolves fairly quickly in the water. This then rusts the inside of the rads. The nitrogen only dissolves to a small degree.

The manufacturers instructions dont always mention the best operating conditions. Further differences can arise as a result of different operating customs in different countries.

Tony

b33man · 3 Mar 2010

Well thanks for all your helps, its appreciated.

I not changing the settings as we're getting better results than before, offdownt'pub to see if there's any rubbish wit face on't bar.

Cheers

Agile · 4 Mar 2010

I dont know if its true but at vaillant I was told their engineers had a cylinder of NITROGEN for repressurising EXVs to avoid the problems caused by adding firther oxygen.

Tony

b33man · 4 Mar 2010

Nitrous oxide (N2O) "laughing gas", it was found capable of inducing a state of social disinhibition resembling drunkenness.

Also used as an anesthetic, something Vaillant engineers need to work on their kit.
I didn't sayit!

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biasi combi boiler m90f.28s slowly losing CH pressure...?

DeltaT

DeltaT

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