Air getting into water system

[Johntheo5]

Very interesting Tony.

Apart from the noise, I see that the pump is (I'm fairly sure) in Auto Adapt mode, while this shouldn't cause noisy operation, I have never seen a Grundfos pump up to now running even remotely at a fairly sensible power output, most pump (Auto Adapt) nothing at ~ 9W.
However, the main problem is that its impossible to calculate the pump head and flowrate from this but in your first photo of the pump, below, it shows it running in constant pressure mode 1, CP1, which is a constant pressure of 3M and, from the pump curves, gives a flowrate of 10.0LPM, pretty normal IMO, the mystery is why is the pump running in CP mode when on CH duty and Auto Adapt mode in HW duty, as far as I know these modes are only selectable manually with the setting button.

So, if, just now on CH duty only, press and hold that setting button, the LEDs should then start highlighting in sequence from III,II,I (on the left of AutoAdapt) and then to the right, when the third LED (like below) on the right is highlighted, release the setting button, the pump will now be in CP1 mode which at 3M should certainly not be the cause of any pump over/air ingress. (I run mine at the equivalent of 3.6M which flows 12LPM).
The setting button is on the very bottom, >

When HW is next requested/required then the pump should stay in CP1 mode and the flow rate can then be calculated from the power output.

If its running just now on the CH you might just post another photo of the Pump+LEDs.

If I am not reading the LED properly in the video and it is running in CP1 mode then the power falls to 14W to give a flowrate of only 3.0LPM, definitely air in the system.

EDIT: Looking at that video again then yes, I think it is running in CP1 mode (third LED on the right) so no need to reset it.

You might also check that bypass valve in the attachment, these valves take ~ 3 to 4 full turns of the handwheel to fully open or shut, it may be partially or fully open so try turning it clockwise first and count the number of full turns to shut it, if its fully shut it will take 3 or 4 turns to fully open it, if so, shut it again and leave it shut.

 

[DP]

12 rads, we specced the new boiler about six years ago, to cope with this many

It is not the number of radiators that matter, what is required is the total output, then size the boiler for that and cylinder. Lot of boilers will provide dual outputs, one for cylinder and another for boiler

 

[bilbobaggins88]

Very interesting Tony.

Apart from the noise, I see that the pump is (I'm fairly sure) in Auto Adapt mode, while this shouldn't cause noisy operation, I have never seen a Grundfos pump up to now running even remotely at a fairly sensible power output, most pump (Auto Adapt) nothing at ~ 9W.
However, the main problem is that its impossible to calculate the pump head and flowrate from this but in your first photo of the pump, below, it shows it running in constant pressure mode 1, CP1, which is a constant pressure of 3M and, from the pump curves, gives a flowrate of 10.0LPM, pretty normal IMO, the mystery is why is the pump running in CP mode when on CH duty and Auto Adapt mode in HW duty, as far as I know these modes are only selectable manually with the setting button.

So, if, just now on CH duty only, press and hold that setting button, the LEDs should then start highlighting in sequence from III,II,I (on the left of AutoAdapt) and then to the right, when the third LED (like below) on the right is highlighted, release the setting button, the pump will now be in CP1 mode which at 3M should certainly not be the cause of any pump over/air ingress. (I run mine at the equivalent of 3.6M which flows 12LPM).
The setting button is on the very bottom, >

When HW is next requested/required then the pump should stay in CP1 mode and the flow rate can then be calculated from the power output.

If its running just now on the CH you might just post another photo of the Pump+LEDs.

If I am not reading the LED properly in the video and it is running in CP1 mode then the power falls to 14W to give a flowrate of only 3.0LPM, definitely air in the system.

EDIT: Looking at that video again then yes, I think it is running in CP1 mode (third LED on the right) so no need to reset it.

You might also check that bypass valve in the attachment, these valves take ~ 3 to 4 full turns of the handwheel to fully open or shut, it may be partially or fully open so try turning it clockwise first and count the number of full turns to shut it, if its fully shut it will take 3 or 4 turns to fully open it, if so, shut it again and leave it shut.




View attachment 335429

Just seen your edits. May I ask what purpose the bypass valve and pipe serves? If it's shut, what is it preventing please?

 

[Johntheo5]

it may be providing a minimum flow through the boiler when both the CH & HW motorised valves shut, the boiler then stops firing but the circ pump continues to run (overrun) for a few more minutes to cool down the boiler heat exchanger, a automatic bypass valve (ABV) is very often installed but some boilers have a internal bypass which on some gives the necessary flow without the need for a external bypass.

 

[Johntheo5]

You have a heat only boiler (external pump) so it won't have a internal bypass, if you had a ABV, it would have been installed where that manual valve is shown and would look something like this, below.
Its easy to check if that manual bypass is open, just feel the pipe its on at around mid length, it will be very hot if the bypass is open, cold if shut.

 

[bilbobaggins88]

Plumber has just spent 3 hours onsite, diagnosing this air problem. Pump replaced (second time in 11 years we've been here), he said the impeller was in pieces??, yet still there is much air circulating when on hw cycle. When we switch to CH and HW we get very little air noise.

After checking tanks, which he believes are setup fine, he's now suggesting a pin hole in the cylinder coil and various methods to test this such as that we don't use hot water taps and see if the level in the expansion tank goes up, which it shouldn't, but does suggest a feed of water from the main tank?

He's pretty sure of the cylinder problem having put his ear to it when air starts to move around and is suggesting £350 parts and a day's labour inc replacing a couple water tank parts whilst system is drained down.

He also mentioned that the bypass is crude/lazy and could be replaced with a flap mechanism, but without recording what he says, I can't say for sure.

He also thinks the return on the boiler is strong enough suggesting that the boiler is not congested or blocked, but we'd notice that when on the CH cycle only I guess too?

My worry is that there's no guarantee a cylinder replacement will fix it.

 

[dilalio]

Plumber has just spent 3 hours onsite, diagnosing this air problem. Pump replaced (second time in 11 years we've been here), he said the impeller was in pieces??, yet still there is much air circulating when on hw cycle. When we switch to CH and HW we get very little air noise.

After checking tanks, which he believes are setup fine, he's now suggesting a pin hole in the cylinder coil and various methods to test this such as that we don't use hot water taps and see if the level in the expansion tank goes up, which it shouldn't, but does suggest a feed of water from the main tank?

He's pretty sure of the cylinder problem having put his ear to it when air starts to move around and is suggesting £350 parts and a day's labour inc replacing a couple water tank parts whilst system is drained down.

He also mentioned that the bypass is crude/lazy and could be replaced with a flap mechanism, but without recording what he says, I can't say for sure.

He also thinks the return on the boiler is strong enough suggesting that the boiler is not congested or blocked, but we'd notice that when on the CH cycle only I guess too?

My worry is that there's no guarantee a cylinder replacement will fix it.

Well. He spent 3 hrs on site and is a plumber. So he has a much better handle on it that anyone else.

It's down to you and your faith in him.
That's the nature of things.

Life don't come with a guarantee.

 

[bilbobaggins88]

Another plumber rang me when I said I'd found someone, and queried whether our Aqua Lisa power shower has a Surrey flange between it and the cylinder. No is the answer.

Also, the phenomenon when two hot taps compete with each other and splutter, might suggest pour flow into the loft tanks.

Also, if there was a hole in the cylinder coil, wouldn't I have slightly brown water coming out of my taps?

Hmmmm

 

[dilalio]

whether our Aqua Lisa power shower has a Surrey flange between it and the cylinder. No is the answer.

Well, that's new info.
Certainly worth investigating.

 

[bilbobaggins88]

Shower pump doesn't draw off a Surrey flange by looks of it

 

[Johntheo5]

But they are two different problems, air in the CH system has nothing to do with air in the showering/hot taps system.

Did your plumber slacken off the coil inlet (top) compression nut and pull back on the pipe to check for air??, I would be very slow throwing a new cylinder at it, at the very least, confirm or not that the coil is holed.

Is the replacement pump the same make/model?, Grundfos Alpha2.

Did you check if a ABV is installed, if so, what is it set to?.

 

[dilalio]

But they are two different problems, air in the CH system has nothing to do with air in the showering/hot taps system.

Did your plumber slacken off the coil inlet (top) compression nut and pull back on the pipe to check for air??, I would be very slow throwing a new cylinder at it, at the very least, confirm or not that the coil is holed.

Is the replacement pump the same make/model?, Grundfos Alpha2.

Did you check if a ABV is installed, if so, what is it set to?.

Tbh, I forgot what the thread was about. As above. 2 separate systems!
But... Compromised if coil is holed... This then joins the 2.

 

[bilbobaggins88]

But they are two different problems, air in the CH system has nothing to do with air in the showering/hot taps system.

Did your plumber slacken off the coil inlet (top) compression nut and pull back on the pipe to check for air??, I would be very slow throwing a new cylinder at it, at the very least, confirm or not that the coil is holed.

Is the replacement pump the same make/model?, Grundfos Alpha2.

Did you check if a ABV is installed, if so, what is it set to?.

Hi John, he said he slackened the auto breather nut, and said they were prone to leaking so I think that's shut.

He installed a pump from a respected local firm "Stuart turners", it's lost the LED display that I had on the Grundfos. I was sceptical about the pump as it wasn't that old.

Sorry didn't ask about the ABV, didn't want to teach the guy to suck eggs.

The surrey flange on the shower had me interested as my wife used that Aqua Lisa a lot more (she prefers baths) at start of year, and that's when we first had the boiler quit on us due to air.

Isn't the second plumber correct in that a hole in the coil would lead to tap water being discoloured?

Thanks!

 

[dilalio]

Isn't the second plumber correct in that a hole in the coil would lead to tap water being discoloured?

Yes. But depends how big the hole is and how much is crossing over! But generally, this is a sign... As is cwsc filling up if no hot water is drawn off.