expansion tank pessure advice

[joesoap1]

Hi, I want to check my pressure in my expansion tank, can this be done accurately without draining boiler or reducing pressure.As I am about to put Fernox F4 into system, due to untracable leak, the perssure now stands at 0.5 bar, and does not go below.So can I assume pressure in tank should read 1.5 bar to be correct? 1+0.5.Or would I be better off reducing preesure to 0, before checking pressure.also, as I am putting F4 into system that has NO inhibitor in, not for last 15 years,would I gain by adding some at same time as F4, later when/if leak is sealed, or not at all, without flushing first?OR not at all per se;

 

[nickso]

confusing post.

i find it best to match the water pressure and EXV pressure as close as possible. put 1 bar into the EXV and i put 1.2(ish) bar of water in. i put 1.2 bar in as most customers turn into dribbling buffoons when it comes to water pressure and assume that if the pressure drops even a needles width below 1 bar there is a fault and they need to fill it to 10 bar or call me for an unnesscessary recall.

you cannot accurately fill the EXV without taking the pressure off the system and leaving an open end. check the FAQ for the correct procedure.

you may find your leak is attributed to to the flat EXV as if it has 0.5 bar in it with water pressure in the system it will have 0 bar in it when you drain the water pressure. you can put inhibitor in at the same time if you wish but i would stick to the same manufacturer. only use leak sealer if you absolutely have to.

 

[joesoap1]

confusing post.

i find it best to match the water pressure and EXV pressure as close as possible. put 1 bar into the EXV and i put 1.2(ish) bar of water in. i put 1.2 bar in as most customers turn into dribbling buffoons when it comes to water pressure and assume that if the pressure drops even a needles width below 1 bar there is a fault and they need to fill it to 10 bar or call me for an unnesscessary recall.

you cannot accurately fill the EXV without taking the pressure off the system and leaving an open end. check the FAQ for the correct procedure.

you may find your leak is attributed to to the flat EXV as if it has 0.5 bar in it with water pressure in the system it will have 0 bar in it when you drain the water pressure. you can put inhibitor in at the same time if you wish but i would stick to the same manufacturer. only use leak sealer if you absolutely have to.

Hi, sorry if I confused you, but you havealso confused me. My pressure on the boiler is reading 0.5 bar.due to the leak.no piont going to 1 bar as after 2 days it.s back to 0.5 bar.As exv should have 1.bar of air in, does that mean, my bike pressure guage should read 1.5 bar.0.5 of water.pressure+0.5 of air? I am only interested in the AIR side of exv reading.not the water side.

 

[nickso]

you cannot be interested in one side only as they are inextricably linked. there is no point in measuring the EXV pressure with water pressure in the system, you will not get an accurate reading.

you must remove the water pressure and leave an open end. then measure the EXV and set it to 1 bar. then reset your water pressure to your preferred pressure, i prefer 1.2 bar.

it's the only way to do it properly.

 

[joesoap1]

you cannot be interested in one side only as they are inextricably linked. there is no point in measuring the EXV pressure with water pressure in the system, you will not get an accurate reading.

you must remove the water pressure and leave an open end. then measure the EXV and set it to 1 bar. then reset your water pressure to your preferred pressure, i prefer 1.2 bar.

it's the only way to do it properly.

Hi, Thanks ,That,s just what I needed to know. Sorry i I confused matters.Rearding the sealant F4, As I have been unable to locate the leak, over years,I don,t see any alternative but use a sealant, or just run boiler @ 0.5 bar,which it is happy with. Unless you have any other suggestions.The reason there is no inhibitor in, is because of years of continuous topping up.The reason I ask if both sealant and inhibitor can be added together is because I have to have open end as you say, to check exv, so that,sbest time to put sealant in, and inhibitor.Via the loop.Correct???

 

[TicklyT]

It is the VOLUME of air in the expansion vessel that is significant, and the only way to check that is to drop the pressure on the water side to zero first. The precharge pressure is there to clear all the water out of the vessel when the system is cold, leaving space for expansion when it heats up.

Attempting to re-pressurise an expansion vessel without dropping the system water pressure just leaves the expansion vessel full of water instead of air, but with the water at a higher pressure than it was before.

 

[joesoap1]

It is the VOLUME of air in the expansion vessel that is significant, and the only way to check that is to drop the pressure on the water side to zero first. The precharge pressure is there to clear all the water out of the vessel when the system is cold, leaving space for expansion when it heats up.

Attempting to re-pressurise an expansion vessel without dropping the system water pressure just leaves the expansion vessel full of water instead of air, but with the water at a higher pressure than it was before.

Hi, Thanks, that's what I wasn't sure of. That's why I asked if both, inhibitor and F4 sealant can be put in together when system has no pressure in it , when checking exv aiir pressureNot sure if 1 conflicts with other.Tryin to do 3 things in 1 go.?

 

[Master of None]

Sounds like your expansion vessle is flat. Dont add sealer untill you have checked that this is not the case.
1 topup cold system to 1.5 bar.
2 turn on heating to high.
3 watch preasure rise.
If it gets close to 3 bar check outside for water being ejected from safety valve. (Do not look into end of pipe)
To put air in.
1 Let system cool
2 remove a rad bleed screw on a rad which is NOT isolated.
3 start pumping air into exp ves (this will take some time with a hand pump). Water will be ejected from bleed screw.
4 After you have stopped for several rests you will start to feel some resistance to pumping and water will stop being ejected. Others have already advised on pressure.
5 replace bleed screw and dust cap.
6 Run system

I am not a pro so any one please correct my advise.

 

[joesoap1]

Sounds like your expansion vessle is flat. Dont add sealer untill you have checked that this is not the case.
1 topup cold system to 1.5 bar.
2 turn on heating to high.
3 watch preasure rise.
If it gets close to 3 bar check outside for water being ejected from safety valve. (Do not look into end of pipe)
To put air in.
1 Let system cool
2 remove a rad bleed screw on a rad which is NOT isolated.
3 start pumping air into exp ves (this will take some time with a hand pump). Water will be ejected from bleed screw.
4 After you have stopped for several rests you will start to feel some resistance to pumping and water will stop being ejected. Others have already advised on pressure.
5 replace bleed screw and dust cap.
6 Run system

I am not a pro so any one please correct my advise.

Hi, Sorry but not so. I didn't think pressure in exv was flat.80c Max setting on boiler. showing 1 bar from 0.5 bar , just 0.5 bar rise. I have searched for years to find the leak without success.Wierd how it runs fine @ 0.5 bar, but increase it and it just discharges it somewhere, with no sign of leak.within 2 days, then happily plods along at 0.5 bar. hence sealant.If it was going into exv, it would be full now and blowing off at PRV the times I have topped it up over the years, Dozens and dozens.PRV is dry, no discharge at all.

 

[joesoap1]

Sounds like your expansion vessle is flat. Dont add sealer untill you have checked that this is not the case.
1 topup cold system to 1.5 bar.
2 turn on heating to high.
3 watch preasure rise.
If it gets close to 3 bar check outside for water being ejected from safety valve. (Do not look into end of pipe)
To put air in.
1 Let system cool
2 remove a rad bleed screw on a rad which is NOT isolated.
3 start pumping air into exp ves (this will take some time with a hand pump). Water will be ejected from bleed screw.
4 After you have stopped for several rests you will start to feel some resistance to pumping and water will stop being ejected. Others have already advised on pressure.
5 replace bleed screw and dust cap.
6 Run system

I am not a pro so any one please correct my advise.

Hi, Sorry but not so. I didn't think pressure in exv was flat.80c Max setting on boiler. showing 1 bar from 0.5 bar , just 0.5 bar rise. I have searched for years to find the leak without success.Wierd how it runs fine @ 0.5 bar, but increase it and it just discharges it somewhere, with no sign of leak.within 2 days, then happily plods along at 0.5 bar. hence sealant.If it was going into exv, it would be full now and blowing off at PRV the times I have topped it up over the years, Dozens and dozens.PRV is dry, no discharge at all.

UPDATE.HI, JUst topped up to 1.5 bar, on max 80c+ and pressure levelling @ 2.4bar, no blow off @ PRV.Looks Like Exv is not flat, ;May need a bit in?

 

[misterdubya]

Its flat. That is unless your heating system is so big, you need a remote vessel fitting aswell, or your communication tube is blocked.

Mr. W.

 

[joesoap1]

Its flat. That is unless your heating system is so big, you need a remote vessel fitting aswell, or your communication tube is blocked.

Mr. W.

Hi, How do you work that out, theres still 0.5 bar spare.I.ve only got 4 of 13 rads going at present.please explain FLAT. To me that means no air in?

 

[misterdubya]

How do you work that out

I dont need to, the difference in system pressure makes it plainly obvious.

theres still 0.5 bar spare.

Spare? If your talking about system pressure you are veering off on a tangent. Im talking about expv pre-charge pressure.

I.ve only got 4 of 13 rads going at present.

So, with ONLY 4 rads your 1.5 bar is going up to 2.4 bar with a hot system. Open up all 13 and then re-heat the system with 1.5 bar system pressure. You'll be at 3 bar in no time.

please explain FLAT. To me that means no air in?

Correct, either the diaphragm has split and its full of water (easy to test - push the pin in on the shraeder valve and if water comes out if knackered), or nothing will come out and your lucky and it can be repaired. Read the FAQ's on the procedure (or this thread).
BUT, if the expv has the correct pressure and your system pressure is swaying as much as yours then the tube connecting the expv to the system is blocked.

So, based on the advise by all thats given, what do you know about your expv? You must have tested it, so Im going for the latter comment. If you have not, please do before you report back.

Mr. W.

 

[Master of None]

Its flat. That is unless your heating system is so big, you need a remote vessel fitting aswell, or your communication tube is blocked.

Mr. W.

Hi, How do you work that out, theres still 0.5 bar spare.I.ve only got 4 of 13 rads going at present.please explain FLAT. To me that means no air in?

Unless all rads are open you are not seeing the true full expansion of the system, most of the water in the syatem is still cold.
Also to get a 1 bar bressure increase with just 4 rads you have an expansion issue. Get all rads open at full temp and watch pressue and PRV discharge. Everything you have said sugests to me PRV discharge. I am no expert but this is how it seems to me.

 

[Master of None]

Bugger
misterdubya beat me to it.
But you will see we are both thinking along the same lines.