Pressure drops when 650 litre buffer tank is filled with water but no drop with air

[Trevor Rix]

I have a 70kW woodchip biomass boiler installation including a 650 litre buffer tank, all installed in 2014. The buffer tank loses pressure from say 2.58 bars to 0.00 bars within a 48 hour period. Yet there are no visible signs of any water leaks,

When this tank is drained of water then pressurised with air to 2.40 bars the same pressure gauge mounted at the top does not drop. And when all of the joints etc. are treated with soapy water there are no visible leaks.

There was a similar scenario with a leg of 60m of highly insulated underground pipe that lost pressure when filled with water, but did not lose pressure when pressurised with air. When the air was replaced with water there is still no pressure drop.

It is thought that the system has been losing pressure ever since installation. We have yet to refill the whole system with water/inhibitor and turn the boiler back on.

Suggestions as to what may have caused this phenomenon, and any possible long term cures, are welcome.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

a wild stab in the dark, is the buffer heating a dhw cylinder? maybe a leak on the coil?

Could you please read the whole thread.

 

[devoncreamy]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

have scan read, my apologies. good luck

 

[missplumb]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

what volume is the buffer?, why are you cold filling to 2.5 bar, should only be about 1 bar, possibly 1.5 for system with Kamstrup heat meter. only having 0.5 bar expansion on a system of 3000 ltrs is very likely to cause is to blow off. It doesnt take much of a leak at 80 degrees to lose that much pressure, and it will evaporate quite quickly. Also looking at pic 4, the strainer is upside down. Im not sure what the water regs are in Suffolk but in North Yorks, any system over 45kw is required to have an automatic filling system.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

what volume is the buffer?, why are you cold filling to 2.5 bar, should only be about 1 bar, possibly 1.5 for system with Kamstrup heat meter. only having 0.5 bar expansion on a system of 3000 ltrs is very likely to cause is to blow off. It doesnt take much of a leak at 80 degrees to lose that much pressure, and it will evaporate quite quickly. Also looking at pic 4, the strainer is upside down. Im not sure what the water regs are in Suffolk but in North Yorks, any system over 45kw is required to have an automatic filling system.

Sorry for the slow reply. I did not receive a notification. Thanks for your observations.

The buffer is 650 litres. I am the customer/end user, not the installer/plumber. The pressure switch now installed (not shown in photos) is set to inactivate the boiler at 0.6 bars, so 1.0 bars would not provide much leeway. The installers decide on the pressures for testing purposes, not me. I think the normal operating target is 1 to 2 bars, the upper limit being the blow off point on the buffer of around 2.8 bars. The heat meters are Sontex.

Where do I find the strainer are you referring to? I did not know there was one.

Are saying that there should be an automatic topup of mains water if the pressure drops too low? I have not heard of that before.

 

[trplumb]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Sorry for the slow reply. I did not receive a notification. Thanks for your observations.

The buffer is 650 litres. I am the customer/end user, not the installer/plumber. The pressure switch now installed (not shown in photos) is set to inactivate the boiler at 0.6 bars, so 1.0 bars would not provide much leeway. The installers decide on the pressures for testing purposes, not me. I think the normal operating target is 1 to 2 bars, the upper limit being the blow off point on the buffer of around 2.8 bars. The heat meters are Sontex.

Where do I find the strainer are you referring to? I did not know there was one.

Are saying that there should be an automatic topup of mains water if the pressure drops too low? I have not heard of that before.

Automatic top ups can introduce fresh water into your sealed heating system and causes oxidising(very bad). U needa sort out the leak!!!!
1.. If xpan ves is set at 1.5bar then your sealed system should be the same pressure. Pres drops can be caused by any one of your blow offs(exp relief valves) expelling water through pipework to outside where it cant be noticed(check tundish is dry). Blow offs arent accurate(less 3bar)
2..One off isolating valves letting water through when meant to be closed.
3..Pin hole in any coil fitted to buffer.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Automatic top ups can introduce fresh water into your sealed heating system and causes oxidising(very bad). U needa sort out the leak!!!!
1.. If xpan ves is set at 1.5bar then your sealed system should be the same pressure. Pres drops can be caused by any one of your blow offs(exp relief valves) expelling water through pipework to outside where it cant be noticed(check tundish is dry). Blow offs arent accurate(less 3bar)
2..One off isolating valves letting water through when meant to be closed.
3..Pin hole in any coil fitted to buffer.

There are no automatic top ups.

What leak? The problem is that there was no leak. There were unexplained pressure drops, fast enough drops to switch off the boiler within a couple of days, that stopped dropping during testing when air replaced the water. The whole system is now filled with water and is up and running with everything connected and working.

There are only two blow offs, one on the buffer tank, and one on the boiler in case of excess heat. They are not blowing off.

There are no isolating valves that are turned off.

There are no coils.

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Is this still going on ?
I've not looked at this thread for weeks.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Is this still going on ?
I've not looked at this thread for weeks.

It's still going on in the sense that the cause of the drops in pressure is unresolved. It's as if replacing the water with air magically stopped the pressure drops. This is logically not possible. No one who has looked at the system and no one in this thread has come up with a plausible explanation.

The system is now working and is being monitored for pressure drops. So far so good.

 

[ShaunCorbs]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

It's still going on in the sense that the cause of the drops in pressure is unresolved. It's as if replacing the water with air magically stopped the pressure drops. This is logically not possible. No one who has looked at the system and no one in this thread has come up with a plausible explanation.

The system is now working and is being monitored for pressure drops. So far so good.

have you pressure tested the system yet?

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Wierd !

Air will obviously contract a lot. So the temperature of air put in, once stabilised will drastically change pressure just like testing a large gas installation but you've thought of that ?

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

have you pressure tested the system yet?

Please read the whole thread.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Wierd !

Air will obviously contract a lot. So the temperature of air put in, once stabilised will drastically change pressure just like testing a large gas installation but you've thought of that ?

I am not sure I follow what you are saying. How is that relevant?

 

[ShaunCorbs]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Please read the whole thread.

I have also you haven't tested the whole install only sections which is not good enough

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

I have also you haven't tested the whole install only sections which is not good enough

Only two sections dropped pressure so it was those two sections that were most intensively tested.

To be clear, the pressure drops occured when the system was filled with water. The sections that were losing pressure stopped losing pressure when that water was replaced with pressurised air. When that pressurised air was replaced with water there continued to be no pressure drops.

 

[ShaunCorbs]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Only two sections dropped pressure so it was those two sections that were most intensively tested.

To be clear, the pressure drops occured when the system was filled with water. The sections that were losing pressure stopped losing pressure when that water was replaced with pressurised air. When that pressurised air was replaced with water there continued to be no pressure drops.

For a start you can't pressure test with air anything over 0.5 bar needs to be water

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

For a start you can't pressure test with air anything over 0.5 bar needs to be water

Well, the reason for testing with air was that there were no visible water leaks. So air was tried to see if bubbles appeared in the exposed underground pipework that was covered with water.

The result was unexpected. No more pressure drops!

 

[ShaunCorbs]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well, the reason for testing with air was that there were no visible water leaks. So air was tried to see if bubbles appeared in the exposed underground pipework that was covered with water.

The result was unexpected. No more pressure drops!

I've had fittings tested on air and no leaks come to water test leak so get your plumber to test the whole system to 10 bar water and leave it for half a day (if you can't 2-3 hours will do)

soon see what's at fault

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

I am not sure I follow what you are saying. How is that relevant?

If the air you pump into the system is, for example at 21 deg or room temp and you push it into buried pipes, that are say 12deg ( in the ground), the air will contract a lot as the temperature stabilises.

This will give the impression that you're loosing pressure when you're not.

i don't know if they waited when testing with air or give it up straight away.

To me it sounds like that's what happened. You said you had no leak when filled with water !

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

If the air you pump into the system is, for example at 21 deg or room temp and you push it into buried pipes, that are say 12deg ( in the ground), the air will contract a lot as the temperature stabilises.

This will give the impression that you're loosing pressure when you're not.

i don't know if they waited when testing with air or give it up straight away.

To me it sounds like that's what happened. You said you had no leak when filled with water !

Unfortunalely you have not understood what I have written in this thread. Your comments are therefore irrelevant.

There was no pressure drop when air was in the system, nor when the air was replaced with water.

The testing with air took place over several days.

 

[Last Plumber]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well Trevor,
I have read the thread and commented throughout.
I am only trying to offer suggestions to the ridiculous sounding situation you're in.

It has gone on a while now and I admit I've kind of lost where we're up to.

For the life in me, I don't understand why your installer hasn't solved this by now. It is extremely difficult reading threads and other people's posts, in trying to solve a problem like this
I.e. Not physically dealing with it.

All that said, I understand that you think my comments are 'irrelevant '.

I wish you luck with this. I hope you get to the bottom of it soon.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Well Trevor,
I have read the thread and commented throughout.
I am only trying to offer suggestions to the ridiculous sounding situation you're in.

It has gone on a while now and I admit I've kind of lost where we're up to.

For the life in me, I don't understand why your installer hasn't solved this by now. It is extremely difficult reading threads and other people's posts, in trying to solve a problem like this
I.e. Not physically dealing with it.

All that said, I understand that you think my comments are 'irrelevant '.

I wish you luck with this. I hope you get to the bottom of it soon.

Thanks for taking the trouble to respond. It was only your last comments that I felt were irrelevant.

The installer has not solved the cause of the pressure drops. They are as puzzled as everyone else.

 

[SimonG]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Time to get the manufacturer of the pipe system involved.

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Time to get the manufacturer of the pipe system involved.

Uponor were involved a long time ago. They say that their pipe does not leak. But if a leak is found they would investigate. No leak has been found.

 

[SimonG]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Does the system have automatic air vents. Is the underground pipe dead level?

 

[Trevor Rix]

Re: Pressure drops when 650 litre buffer tank is filled with water but no drop with a

Does the system have automatic air vents. Is the underground pipe dead level?

Yes there are some automatic air vents, but the red plastic caps are screwed closed.

No, the underground pipe is not dead level.