Air being drawn into shower pump

[Marky_Mark]

Hi guys

We have a gravity fed hot water system in our bungalow heated indirectly by an oil boiler.
We have two shower pumps. One pump feeds one bathroom (the shower and bath) and the other pump feeds the other bathroom (the shower, bath and the hot feed to the bidet and sink). Non-pumped hot supply to other two sinks.

We recently changed the kitchen tap (non-pumped) and found the hot flow was pretty poor. So we had this tap swapped from the non-pumped hot supply to the pumped supply shared with one of the bathrooms (the one with the pumped bidet and sink).

There now appears to be air getting into the system. This was never a problem before. Interestingly, this is happening to both pumps! The showers tend to only last a couple of minutes before slowing down and stopping completely. The hot water sometimes doesn't come out of the taps at all. Air is coming through. After we've used hot water, the pump sometimes starts and stops on its own. We can use the showers by making sure they are set to slow flow only.

I initially thought air was trapped in the system but it seems like new air is being drawn in. Not sure what the problem could be or what to do. The guy who did the job is coming back next week.

All thoughts and advice appreciated!
Mark

 

[motorbiking]

Can't see the rating of the pumps you have or the dimension of your feed pipe from your hot water, but its likely that you are either drawing air in from your supply tank or you are causing too much low pressure which causes bubbles to form. There is a realistic limit that you can supply on a gravity fed system.

 

[Gasguru]

Those pumps should cope with significant air to there's a straightforward problem somewhere.
Check the water level in the cold water cistern when the problems start, pull out the cylinder flange and check for scale etc.
Are those pumps designed for single tap operation...only certain models are. (Seals can pop under pressure from churn on the dead headed impeller end)

 

[Marky_Mark]

Thanks for the replies. I will take a photo of the pumps later.

The cold water tanks are massive and have plenty of water in them. I think one tank feeds the cylinder and also the cold feed to one pump. The other tank feeds the cold to the other pump. There is a 3rd tank for the heating.

I just can't understand why everything has worked no problem until this change was made. There is a faulty shut-off valve to the cylinder, it just spins round, so I'm wondering if the guy tried to use it and now it's partially obstructing the flow. Or maybe some other kind of restriction of water from the cold tank to the hot tank, causing air to be drawn down through the vent. Does this seem like the most likely option?

I can't figure out if the problem is purely because of swapping one tap from non-pumped to pumped (unlikely?) or if it's actually something else. Especially considering that the shower on the other pump is having the exact same problem, when that pump/circuit wasn't touched.

 

[Gasguru]

Start with the "faulty shut-off valve"...if the water is restricted the pumps could be pulling air down the cylinder safety vent pipe.

 

[Marky_Mark]

Here are the shower pump and valve photos. I am not confident to change the valve myself, so I will need to get someone to do that. I have tried calling another local plumber that I've used before but no reply yet. Thanks for the help!

 

[Marky_Mark]

UPDATE! All fixed!

It turned out that the gate valve was the culprit. Here of some photos of it in its open position! Amazing that any water at all was finding its way through. Replaced and all is fine now.

Thanks, guys!

 

[Gasguru]

That's surprising given it's a high quality Pegler valve. Take the headgear off and see if the spindles sheared.
Of course some plumbers have no finesse and instead of working the spindle back and forth and loosening the gland seal they go at them with full force.
I'd check with Stuart Turner...some of these shower pumps are not designed to run just a single hot or cold tap alone.
The closed side of the pump can be damaged as the water churn raises the temperature and the resulting pressure increase pops the seals.
Pumps designed for "dead-heading" as it's known have bypasses across the inlet/outlet AFAIR.