Secondary Return Pump Noise / Air ?

[bwel]

Hi,
Recently I noticed that we were running out of HW more than expected, perhaps it’s people are taking more baths but I wanted to check out if the pair of Vaillant uniSTOR’s were both heating, thinking that maybe I had a problem with one of the Zone Valves were not heating one of the tanks.

Felling the Hot Flows, both uniSTORE tanks are fully heated.

So then I thought, perhaps I’m just losing more heated water with the Secondary Return flow in this cold season. So in looking at the Secondary Circulating AutoAdapt pump, I changed the mode from Auto through Temp and 100%. This started the pump, but it does not sound right now, possibly air or something else ?
Flow via all the taps and showers is good, so I’m not sure how I could have air that part of the secondary flow pipes.

The sound in the video below the picture is my unplugging and plugging in the Grundfos Secondary Flow Pump.

Anybody heard anything like this ?

 

[bwel]

Did a bit more investigation today and I don’t think the problem is with the Comfort Pump or Air, but the Check Valve after the Comfort Pump and feeding via a Caleffi Cold Water Control Valve Manifold to the uniSTOR Tank.

Has anybody else seen problems with noisy Check Valves / NRV’s in Secondary Hot Water Circuits ?

 

[ShaunCorbs]

Yea sometimes they go bad

Best to replace to see if it sorts your issue

 

[bwel]

Yea sometimes they go bad

Best to replace to see if it sorts your issue

Thanks Shaun,

Any thoughts on which type to go with: Non Return Valve, Single Check Valve, Double Check Valve...
I read on another thread that there is risk that the Grundfos Comfort Pump may have restricted pressure to pass through the NRV, but I’m not sure which type has the least passing resistance ?

 

[ShaunCorbs]

Single check or a swing check

 

[oz-plumber]

Where's the valve in relation to the pump and the cold water inlet?
There may be an issue where the valve is located

 

[bwel]

Where's the valve in relation to the pump and the cold water inlet?
There may be an issue where the valve is located

The Comfort Pump is about 1m before the Check Valve and the Check Valve is about 1m before the Cold Water Balancing Manifold. Distances are not big and have bends in there so I’m not sure they could be too different.