Air in pump when heating on?

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
Hi,

After winter and without the heater on, just running the pump, I found a lot of air bubbling out of my returns in the pool and weak flow. I thought I must have a leak on the suction side. Whilst investigating, I started to bleed the air using the valve on top of the filter. After several hours doing this, the air bubble seen in the pump cover disappeared, as did the bubbling at the returns and the flow returned to normal.
Today, the water was at 70 f and the pump running for a second hour. I switched the boiler on and returned less than an hour later to see a big bubble in my pump cover, but no bubbling from returns in the pool.
The heating circuit isn't on the suction side, so...?
This is the second time it's happened this season. Can you get an intermittent leak on suction side? Just seems odd both times it happened when I switched heating on after just running pump daily up until then.
Any help gratefully received. Here's a pic of the plant room attached to the cabin housing the hydrotherapy pool.

 

pooldv

Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
25,179
FL panhandle
It is not unusual to have some air build up when you first start up equipment. If the air dissipates and doesn't return then everything is fine. If it returns daily or gets worse then it is time to track down a leak.

More here, Pool School - Suction Side Air Leaks
 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
Ok, I've checked again and small bubbles are again coming from the returns, so a suction side leak. There were definitely none before, so it's intermittent. Perhaps the leak occurs when hot water expands joints in the suction pipework?

Just had a gander at your pool build, pooldv - N-I-C-E!
 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
I closed the red valve on the main drain feed to the pump whilst it was running, thinking I was thereby isolating the skimmer line. Instantly, the water in the pump basket went below the inlet pipe, so I turned off the pump. Does this confirm that the air is being sucked through the skimmer line, or just that I shouldn't have turned off the main?
 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
Just looked again at my setup and with good flow to the pool (despite the pump only priming to just above the inlet pipe) the water in the skimmer is not flowing over the top of the floating Weir. The weir moves up and down freely with a light touch, but my understanding is that the pump should suck it down a little to establish a flow. Is this further indication of a suction leak on the skimmer line? Shutting off the skimmer doesn't affect the pressure reading on the filter. I think I'll leave the skimmer inlet valve shut and try bleeding the air out of the filter again with just the main drain open, although this seems to take hours. (Is there any reason a bleed valve on the pump lid wouldn't work?) If all the air bleeds out of the pump and stays out, I'll know it's the skimmer line.
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
31,537
Sebring, Florida
the water in the skimmer is not flowing over the top of the floating Weir.
is it sucking air into the skimmer since the water is not flowing? Then the pool water is not high enough.
 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
I bled the air out as before, but this time, with the skimmer line shut off, none has returned which is not such a problem, given the pool is in a cabin with only my son, myself and my wife ever using it. Better flow just on main drain anyway.
I could slowly turn on the skimmer and check for air, just to confirm, but I've had enough of bleeding the air out through the filter for now. In fact, because it takes so many uses of the bleeder valve to expel all the air, little by little, it is now leaking a drop a second. Is there an o ring to replace/lube or can I wrap PTFE tape on the thread?

 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
No air in system for an hour before turning heater on. Nothing for first hour of it being switched on, but three hours later, a 2 inch bubble in pump cover. I guess the heat (91 f) has opened up a leak in the main drain? Time to peel the vinyl splashback off and lift the ply cabinet lid to get at the skimmer and main drain pipework. Ho hum!
 

Mattsway

Bronze Supporter
Apr 10, 2017
30
Sussex UK
Silicone lube arrived today, so I used it on the o rings on the pump lid and basket drain valve, the air valve on the filter, the union onto the front of the pump and unions to main and skimmer valves. The lube instantly worked to allow the leaking air valve to seal, but no immediate prime on the pump, so although I'll carry on bleeding the air out as before, I expect it to return little by little.
In doing this job, I realised the cut outs in the cabin wall, bringing the 2 suction pipes in have been cut to the size of the pipe, giving no room for the expansion and contraction of the timber (please see photo above) I reckon the joints I can't yet get at have been compromised by this seasonal movement. We'll see when the builders come to visit.
 

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