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.

 

[Stoney Ground]

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

What are AAVs?

The system is being run at normal operating pressure over the weekend, so no excess pressure is being applied.

Automatic Air Vent (Bleed) as you stated had been fitted, designed to let air out and consequently reduces pressure in the system.

 

[Trevor Rix]

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

Automatic Air Vent (Bleed) as you stated had been fitted, designed to let air out and consequently reduces pressure in the system.

Thanks for the observation. The red plastic cap at the top of the AAV is I think temporarily screwed closed.

 

[voivod]

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

Sorry buffer

 

[Gray0689]

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

In recent testing it was only the buffer tank that was losing pressure. As the buffer tank is isloated from the rest of the system during this phase of testing, any defects within the boiler would be irrelevant.

To recap, there are five sections in the sealed part of the system. (1) boiler (2) expansion vessel (3) buffer tank (4) leg one underground to house (5) leg two underground to a separate building. All five sections has its own pressure gauge. By isolating different sections we should in theory be able to determine which section is losing pressure.

View attachment 27395View attachment 27396View attachment 27397View attachment 27398

Looks like an eta boiler and buffer
Where is the job

 

[Trevor Rix]

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

Looks like an eta boiler and buffer
Where is the job

Yes, it is an ETA boiler and buffer tank. The job is in West Suffolk.

 

[acecharly]

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

Not read through but if theres a vent with a ball in it would float up when full of water but not air.

 

[Trevor Rix]

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

There is no vent and no ball because it is a sealed system as far as the two heat exchangers in the two properties being heated.

 

[acecharly]

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

All I can suggest here is (if you already have not)

1. Isolate each of the 5 sections.
2. Test each section individually (you mentioned earlier testing to 5bar with air I call that a bomb) use water.
3. You should now have narrowed it down to 1 section.
4. Losing that much pressure over that volume of water will be noticeable.
5. If there is pressure loss and no evidence of water then you must have a faulty pressure gauge or that its passing back through any isolation valve you've turned off. So first change the ball valves.

In my opinion and im guessing because like the other guys here im not infront of it, id say your losing it of one of the legs that are out of view or youd see it...only Paul Daniels can make things disappear and im afraid hes no longer an option.

All the best.

 

[devoncreamy]

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?

 

[Trevor Rix]

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

All I can suggest here is (if you already have not)

1. Isolate each of the 5 sections.
2. Test each section individually (you mentioned earlier testing to 5bar with air I call that a bomb) use water.
3. You should now have narrowed it down to 1 section.
4. Losing that much pressure over that volume of water will be noticeable.
5. If there is pressure loss and no evidence of water then you must have a faulty pressure gauge or that its passing back through any isolation valve you've turned off. So first change the ball valves.

In my opinion and im guessing because like the other guys here im not infront of it, id say your losing it of one of the legs that are out of view or youd see it...only Paul Daniels can make things disappear and im afraid hes no longer an option.

All the best.

Could you please read the whole thread.

 

[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