Combo Boiler issues

[Agile]

The air charge pressure is related to the system operating pressure.

In a normal system the boiler is downstairs and its pressurised to about 1.5 bar cold. That allows more scope for minor leaks than any lower pressure.

Putting the air at 0.9 bar means its compressed by the water pressure until it occupies about 2/3 of the EXV volume.

It is thus well able to accept expansion as well as to expel water to maintain the system pressure if there are minor leaks.

Tony

 

[RickH]

I don't think I can physically get to this valve .... even with steps I am going to be too far away to see .... but I'll give it a go tomorrow.
Interesting the manual says in the event of failure it is recommended to install an independent pressure vessel .. rather than try to replace - what a great design. Having a separate vessel is fine as long as the built in one does not start leaking water.

 

[Aquaheat]

There a many many boilers where the EV is mounted at the rear and it is a boiler off the wall job to replace. TBH it doesn't take a great deal of time to do this but the cost of the manufacturers EV and replacement washers for iso's plus the potential for creating other issues it is normally more cost effective and convenient to add an external one on the system and blank off the manufacturers EV if there are leaks.

They can be awkward to get to and sometimes need some contortionist skills but you should be able to get to it. Most of the time we do it blind anyway and just go by feel if they are tight to get to.

Good luck though and let us know how it goes.

Jon

 

[RickH]

OK ... 'maybe' good news.

OK .. nothing wrong with Expansion vessel ... nice dry charge on it, and no water at wrong side of diaphragm.
Noticed the vent pipe was wet ...

So I stripped out the PRV .... was a bit of crud in it, cleaned and on reassembly & refill found the auto air bleed was actually locked closed, so air unable to vent from boiler - so resolved that.

Since re-commission has run perfectly - pressure when cold set to 1 bar .. when heats it is just short of 1.5 bar .... which seems far better.


My assumption is the auto vent closed meant air build up ... possibly kettling ... which would trip the PRV and hence drop pressure ..... crud in the valve meant it did not close properly and hence would drop so low that boiler would then not start up.

Guess I'll find out over next 48 Hrs.

 

[RickH]

Bad News - it's back.

Run fine for 48 Hrs .. never going above 1.5bar
My son reported rushing water sound (but could simple be pump) and after next off period would not start up (pressure down to 0.5bar so locked out)
Re-pressurised and run OK for rest of day - then lock out again next day.

No water leak showing in house - and based on amount being used in top up it would be noticeable.


Anybody any other thoughts ?

Thinking about putting in a boiler de-sludging / cleaning compound (Fernox DS40 or F5) and flush through - see if that helps.

 

[Agile]

You don't seem to have checked the vent on the PRV. I would expect it is still leaking if the pressure is falling.

Obviously you have extra terrestrial servicing skills*, but normal boiler engineers just replace any PRV to prevent future leaking which would reflect badly on them as seen by their customers.

Tony




* or are you just ultra mean?

 

[DP]

In a normal system the boiler is downstairs and its pressurised to about 1.5 bar cold. That allows more scope for minor leaks than any lower pressure.

Me not understand. Can you explain please

 

[RickH]

You don't seem to have checked the vent on the PRV. I would expect it is still leaking if the pressure is falling.

Obviously you have extra terrestrial servicing skills*, but normal boiler engineers just replace any PRV to prevent future leaking which would reflect badly on them as seen by their customers.

Tony

* or are you just ultra mean?

I really don't understand the comment "extra terrestrial servicing skills" .... don't know what you mean, is this some forum in-joke ?

I have not witnessed any leak from the vent pipe when I have been there, at the open end of pipe there is some discolouration on wall ... but that could be verdigris of rain on copper.
I'll tape a plastic bag over end of pipe - if it is 'venting' its will blast bag off, or at least fill it with water.


I stripped & cleaned the valve as I did not have one with me ... if I can prove it a faulty (or highly likely faulty) I'll happily change it ........... want to figure out what should be changed before I buy any parts.
Looking at the way its installed ... you cannot simply unscrew valve to replace ... as the vent pipe is fixed .... and prevents turning.
It will mean I need to cut the copper vent pipe ... to remove it, and I had nothing with me to cut it with ... nor any blowlamp to rejoin pipe afterwards.
So at that time at least checking the valve so debris was I thought a sensible step.

However I can happily look to get one and swap it on Tuesday if advice here is that this would be next step ?
Would that be the next best course of action ?

 

[jeff the gasman]

U need a powerflush and gas engineer/plumber. To have proper look at your son's CH. your room stat is fine, it calls for heat and shuts off.
Problem is poor circulation/dirty system = to ex vessel going, pump, divert valve etc,
Check the colour of the water in the system.
If the CH was working before so I guess the design is ok

Not necessarily, don't listen to advice like this.

 

[Agile]

The vent pipe is normally connected to the PRV by a compression joint with an olive. That is unscrewed to disconnect it.

To check if its leaking fill to 1.5 bar when the system is cold and heat up the radiators to about 70 C and see what the pressure increases to and if the PRV is leaking at that pressure.

A plastic bag or condom will collect water from the vent and it can be seen inside after a day or two.

Extra terrestrial skills are those that don't exist on earth but enable a PRV to be cleaned so that it will 100% reseal without any leakage.

Terrestrial engineers* don't usually have those skills so they just change them. They even keep a stock of PRVs and condoms in their van, so like boy scouts, they are always prepared.

Tony


*With the possible exception of one called Dan who can do things no one else can do like only sleeping for three hours a night and never needing to use a ladder.

 

[Aquaheat]

Have you mean on the wine again Tony?

Happy easter.

 

[DP]

Tony you on drugs or something?

For a man who travels by bus, you seem to be very well equipped to carry our ET repairs (you must be able to transport your self into the future to bring along condoms and necessary parts). And carry a condom to assist repairs now that is something only Mr Agile can think of along with bending a gas pipe around soil pipes, instal observation Windows on Isar heat exchangers to quote two ET skills that come to mind

Come down to earth O Great Heating Engineer and teach us lowly dabblers of strange components within white boxes that provide heat and hot water that we earthlings call Combo. Perhaps you will be doing loop-de-loop in your spaceship bus so will not be able to respond with a suitable reply

Where do you put the ladder when you get on the red bus? I have been up all night thinking about it, have used my friend Google, but still in the dark. Blooming heck, I must be stupid. It is the ET skills- you do not need a ladder. You have a special craft

Signed
Tired and no ladder
Dan

 

[AGAS]

tell you what, its been a while since I've carried condoms about

 

[Dan Robinson]

I'm worried what size Johnnies Tony uses that fit over a 15mm PRV

I tend to advise Party balloons. .

 

[Agile]

Whatever you use, it may be necessary to use a rubber band to ensure it does not slip off.

Condoms used to carried in gentleman's wallets.

But thanks to the Post Office you can usually find a rubber band every few metres from a letter box.