Air consistently entering F&E system? Circulation error, Help needed

[Jay1986]

Thats strange re noise since your present head is 4.2M so the head should have been lower with decreaed noise levels on CP1 (3M) and PP2 (3.7M, max), PP2, even though probably a bit weak at ~ 2.5M at say 0.9ms/hr may be worth another go?.

View attachment 289397

Apologies John, I meant the CC speeds, CC2/3 gave more noise than CC1. Yet to try the other speeds which I’m doing today. Last few days have been a crash course in plumbing terminology, does a lower head essentially mean the pump will run at a lower speed?

 

[Johntheo5]

Yes, lower head = lower speed. Constant pressure CP means the pump will vary its speed as the flow demand varies to maintain that constant head.

CC, constant curve, or fixed speed should mean that the pump develops its maximum head with a closed discharge valve, the head should then fall off as the flow increases, all centrifugal pumps work like this but for some reason or other (which nobody seems to know why) all A rated pumps operate for a portion of their CC modes in CP fashion which means that they must increase speed as the flow increases, Grundfos in particular operate in this fashion, you can see it quite clearly in CCI,CCII&CCIII above, so effectively you actually have 5 CP modes and 2 PP modes.

 

[Jay1986]

If you pist pics of the Feed & Expansion cistern and associated pipework it would help to clarify where the connection should be.

Here are a few pics, not easy to see what happens at the back of tank but the feed opening is shown via the arrow.

If it best to maintain the two separate pipes would it be OK to connect these just before pump entry?

 

[Johntheo5]

The pressures around the system are currently favourable to the pump drawing in air. Connecting the feed into the vent enables the 2 pipes to operate at the same pressure (the neutral point) preventing air ingress.
If you take a look in the install manual you will see a diagram of the close coupled feed & vent arrangement. This is better than a combined feed & vent as the air is vented quicker. Again the idea is to keep the pressure at the 2 pipes equal (or very close). These pipes connect just before the pump inlet for safety reasons and to allow the pump to exert its full pressure across the entire system helping to further prevent air ingress.
Currently if the red cylinder balancing valve were to be inadvertently closed the system no longer has the feed pipe connected (when the cylinder 2 port is unenergised) presenting a safety issue.

Agree that the close coupled feed&vent makes it easier when refilling the system, I (combined feed&vent) have a service 1/2 ins gate valve on the filling line to the F&E tank and I just crack it open when refilling after a drain down and don't have any problems after a day or two when I vent the residual air, the system doesn't have any problem in venting during normal operation judging my fact that some of my rads are 40 years old with only the odd drop of inhibitor added.
I know of several cases where the the close coupled (VCP) feed&vent system still got air ingress even when correctly installed on a clean system when the pump head was increased on the installation of more rads and was cured by changing to my exact system where the vent pipe and the cold feed are the same diameter, it will be interesting to see if combining the vent with the 1/2 ins feed above will work.

 

[Jay1986]

I’ve just run the hot water for half an hour on CP1, also found the red gate valve was only 75% open. Definitely less air in the system but the pump still sounds occasionally like there is some running through the pipes/being pulled in

 

[Johntheo5]

I’ve just run the hot water for half an hour on CP1, also found the red gate valve was only 75% open. Definitely less air in the system but the pump still sounds occasionally like there is some running through the pipes/being pulled in

Immerse the vent end in a glass of water to check, also try PP2 if air is being pulled in on CP1, PP1 is useless. Also, sometime, cut a bit off the vent end as it should never be immersed in water.

 

[Jay1986]

HW off, CH on, two rads closest to pump on (and towel expansion rad) and it trips the circulation error within a few minutes, very frustrating. Any ideas what to check next?

 

[Jay1986]

Immerse the vent end in a glass of water to check, also try PP2 if air is being pulled in on CP1, PP1 is useless. Also, sometime, cut a bit off the vent end as it should never be immersed in water.

I’ll try this now. I’d read that about the vent, thought it was long, I’ll add that to the To Do

 

[Jay1986]

Immerse the vent end in a glass of water to check, also try PP2 if air is being pulled in on CP1, PP1 is useless. Also, sometime, cut a bit off the vent end as it should never be immersed in water.

Vent immersed and held in the water for a couple of mins, the water level drops a few mm but then returns to where it was, happens continuously

Oddly the auto vent doesn’t seem to vent anymore air now, perhaps air is not entering but what im hearing is air still circulating in the system?

 

[Johntheo5]

I’ll try this now. I’d read that about the vent, thought it was long, I’ll add that to the To Do

Vent immersed and held in the water for a couple of mins, the water level drops a few mm but then returns to where it was, happens continuously

Oddly the auto vent doesn’t seem to vent anymore air now, perhaps air is not entering but what im hearing is air still circulating in the system?

Quite possible, try venting with boiler/rads off.

 

[Jay1986]

Will do, at the moment the CH valve is not open though so it should just be circulating I the boiler/tank/expansion towel rad?

I’ve just done a vid of the noise:

The magnaclean filter has also been noisy from day one, anyone know if this is normal?

 

[Gasguru]

Your pics don't show the outlet of the F&E cistern but ideally you would join the feed to the safety pipework at that outlet level making sure there is no chance of airlocks from rising pipework etc..
To comply fully with the regs the feed should be upgraded to 22mm (ie the outlet of the cistern and short length of pipework joining the vent).
Despite some other posters describing their own systems you must not have any valve on this feed/safety vent pipe.
I suggest you read up on static pressures/neutral points and the design of open vented systems.