Pressure loss not normal...need help with mystery!

[Mr Lil]

My Ravenheat LS80 Silver Star boiler is becoming a complete mystery. The boiler keeps losing pressure so I have to keep refilling. It works fine when running but gradually the water goes out via the relief outlet in the wall.
I asked here for advice and the PRV being nackered was suggested.
After a fight to get it I have replaced it but the problem is still the same.
When the heating is running I may need to refill the boiler once or twice while it runs its five hour programme.
I looked outside today and saw it dripping out the relief pipe.
The pressure isn't going above 3 bar as it never gets that high.
When the programme finishs for the morning/night it loses the water when its off so when it is due to come on again it doesnt as the boiler needs refilling.
I've asked a few plumber friends and my father in law who's an ex plumber and no one seems to know.
I have checked the pipes etc for leaks and all is well. This problem has been going on for months now and I'm starting to worry that the boiler wont last long at this rate.
Please help. I hope I've explained to the best I can
Paul

 

[ACOperson]

Expansion vessel. Do a search and you will see how to fix.

changing the PRV would probably have been neccessary anyway so dont beat urself up about it...

 

[Mr Lil]

Great....any ideas where it is...I know they have a car type valve on them. Is it at the back of the boiler or separate or are all boilers different??

 

[Softus]

I looked outside today and saw it dripping out the relief pipe.
The pressure isn't going above 3 bar as it never gets that high.

If these two statements are both correct, then you have a faulty PRV.

 

[ACOperson]

Why?

If the pressure gets to AT or above 3 bar then the PRV activates.

If it it dripping then the PRV has activated correctly.

 

[Softus]

Why?

If the pressure gets to AT or above 3 bar then the PRV activates.

Eh?! The OP has said that the pressure doesn't exceed 3 bar.

If it it dripping then the PRV has activated correctly.

Only if the pressure exceeded 3 bar.

 

[Agile]

Mr Lil, did you replace the WHOLE PRV including the brass body ???

I once saw a PRV which was passing at too low a pressure as a result of a "plumber" having changed the head from a different type!

Tony

 

[nickso]

Why?

If the pressure gets to AT or above 3 bar then the PRV activates.

Eh?! The OP has said that the pressure doesn't exceed 3 bar.

If it it dripping then the PRV has activated correctly.

Only if the pressure exceeded 3 bar.

i disagree.....i have seen them drip on lower pressures anywhere between 2.5 to 3 bar. they had not been tampered with and the only explanation i have is the seat/seal was very dirty on all occasions.

not all pressure guages are accurate either.

 

[Agile]

Most PRVs even if new and clean will start to lift at about 2.5 Bar even though they may be rated at 3.5 bar.

A simple spring loaded device has no magic toggle pressure! It starts to lift at about 2.5 Bar and has a nice trickle at 3 Bar.

I have seen three boilers where the filling loop has been left open and the PRV has failed to relieve the pressure enough to prevent the expansion vessel from bursting.

Tony

 

[Softus]

If it it dripping then the PRV has activated correctly.

Only if the pressure exceeded 3 bar.

i disagree.....i have seen them drip on lower pressures anywhere between 2.5 to 3 bar.

So have I. And if yours were rated to operate at 3 bar then they were faulty.

...they had not been tampered with and the only explanation i have is the seat/seal was very dirty on all occasions.

Faulty then.

not all pressure guages are accurate either.

I didn't claim that they were, I just said that they have operated correctly only if the pressure exceeds 3 bar.

Most PRVs even if new and clean will start to lift at about 2.5 Bar...

Yeah - the faulty ones do.

A simple spring loaded device has no magic toggle pressure!

"Magic toggle pressure"? WTF?

I have seen three boilers where the filling loop has been left open and the PRV has failed to relieve the pressure enough to prevent the expansion vessel from bursting.

You've seen three faulty PRVs then.

 

[nickso]

[quote="Softus]

not all pressure guages are accurate either.

I didn't claim that they were, I just said that they have operated correctly only if the pressure exceeds 3 bar.

[/quote]

your original statement assumed the pressure was at 3 bar when the valve opened which it may not be if the guage is not reading the correct pressure.

fair enough on all other points.

 

[Softus]

your original statement assumed the pressure was at 3 bar when the valve opened which it may not be if the guage is not reading the correct pressure.

The only assumption I ever make on this forum is that people can, and do, read. If it's assumptions and/or errors you're after, then perhaps you should look closer to home...

I looked outside today and saw it dripping out the relief pipe.
The pressure isn't going above 3 bar as it never gets that high.

If these two statements are both correct, then you have a faulty PRV.

I didn't state that the pressure was above 3 bar - I clearly wrote if.

The pressure isn't going above 3 bar as it never gets that high.

He didn't say whether he used the boiler gauge or a separate one, nor did he say whether or not the gauge was calibrated. By pointing out that the PRV he'd just fitted is faulty, I implied that at least one of his 'facts' is possibly wrong. New PRVs can be faulty though.

If you want to (or ACOperson or Agile wants to) argue that a PRV which opens at, say 2.8 bar, is within an acceptable range of tolerance, and therefore not faulty, then that's a different matter, but so far none of you has.

 

[nickso]

ok fair enough softus.

my mistake. the prv may well be faulty or as you say within a tolerance range but i have no way of testing that tolerance and have to rely on the boiler guage, if used, which i was merely pointing out may also be faulty.

 

[Softus]

I completely concur.

 

[oilman]

Most PRVs even if new and clean will start to lift at about 2.5 Bar...

Yeah - the faulty ones do. icon_rolleyes.gif

It MAY be the case they are faulty, but in most cases it won't be, as operating below 3 bar is to be expected.

Assuming the valve is quoted as "3 bar", what is the 3 bar? is it the pressure below which it will open, and remain closed below that pressure, or is it the pressure which will not be exceeded? In either case there will be a tolerance for the operating point.

If you look at manufacturers data sheets, you will find the spec is for a given flow rate at the quoted operating pressure, so it will be letting by at a lower flow rate at a lower pressure. ie could start to open at 2.5 bar.

This does not mean that a 3 bar valve which opens at less than 3 bar is faulty.

The fault is mainly pedantry. Best avoided IMO. Or cured by understanding.