Circulaing pump is pulling air via the vernt pipe

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Can anyone advise.

Just fitted a circulating pump to HW tank. Connects the vent pipe (approx 60 cm from tank top) to the drain connection.

When the pump starts up it is fine. However, it collects air and then stop pumping.

I have avoided puttting an essex value in as the top connection already has a power shower and the vent. the power shower is fine.

Should I
a) Get a lower speed pump (this is a CH pump on setting 1 - 35w)
b) Move the connection closer to the tank connection
c) Accept that an essex valve must be installed - route both the powershower and circulating off the inner connection. Vent of the top as standard.

Thanks
Geoff
 
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please show us a photo of the pipe layout, around the pump, and where the feed pipe, and the vent pipe, connect to the other pipework.

Put the vent pipe in a jar of water so you can see if it is sucking.

An Essex connector is irrelevant.

When did you last give the system a chemical clean to reduce sludge and sediment?

What corrosion inhibitors have been used for the last 20 years?

When you fitted the new pump, what steps did to take to ensure a perfect seal on the suction side of the pump?
 
JohnD, I think the OP is referring to the domestic water side and not the CH circulation. OP, what are you trying to achieve?
 
Yes this is HW sid o the tank

Jam Jar idea is great - will give it a go and report - along with a photo.

The tank/pipework have never been chemically cleaned - the tank is about 10 yrs old. We are not in a hard water area, and we have a household water softener feeding the cold tank (and therefore the hot tank)

Trying to achieve
We have solar panels on the house with a load balancer for the HW heating element. When I have spare leccy, the tank element heats the water (for free) whilst keeping me in expert mode. The element then backs off when the water is hot - but only the top of the tank is hot.

The solar power system that drives the tank heating element is able to detect when the heating element backs-off, and will automatically close a relay. That relay is designed to drive standard water circulating pump (or a heater upto 4KWs) so that I can move hot water from the top of the tank to the bottom - The water heating element will then kick back in and will heat more water (for free). So I have the whole tank hot, and not just the top third. My hope is that we will have enough thermal energy stored to be useful that night and the next day (might be cloudy)

I hope this helps.

Thanks for the suggestions so far. Very very helpful.
Geoff
 
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A central heating pump is no good for potable water, you will need to fit a bronze pump and if you follow the instructions that come with the pump it should be self venting.
 
Potable water ? this is the hot water. No matter, it is a bronze pump. I will re-check the instructions.

The pump is certainly pulling air from somewhere and logically it can only be the vent pipe. :?:

The pump works fine when it starts up - but say 10 mins later, it is “on” but not pumping. Bubbles can be heard in the tank. When the pump is turned off more bubbles are heard. Venting the pump (centre screw) releases air and gets it pumping again.
Geoff
 
Potable means drinkable hot or cold, your hot water has air trapped within it, it does not necessarily have to be pulling it down the vent pipe, double check you have the pump mounted correctly as the wrong orientation will trap air.
 
The vent pipe from the cylinder must rise to allow air to escape. The air is de- oxygenation of the water due to heating.
The Venturi effect on some parts of a system can also have this effect.
 
Where are the connections to the pump actually going? Obviously you need some sort of circuit. I can only assume one end to the hot draw off and the other on the cold feed? If so then you may have the pump pumping in the wrong direction. It'll need to be pumping towards the draw off (and therefore vent pipe). Hopefully on the lowest setting that won't cause it to pump over. If it does then you might need an Essex flange to connect it to!
 
Hi
An update

Consulted the installation instructions - the pipe line is horizontal but the pump was slightly tilted up. That is now fixed. A quick test shows it still gets air, but I should leave it running to test it properly. (There is no doubt that it shifts very hot water when it is first turned on.)

I will do the jam jar test tonight and see if I can get a picture too.

Tank connections
Water is taken off the vent pipe. The 22mm vent pipe comes off the tank top and runs horizontally to the wall (about 30cm). An elbow then takes it vertically up into the attic etc. The T connection for the pump is about 30 cm from where that vertical begins. So it is about 60 cms in terms of pipe length from the top of the tank.

The pump then pushes water in through the tank drain connection. This is a simple 15mm T connection to the drain.

Sorry my time was very limited last night. Did not complete all my homework. :oops:

Thanks for the help.
Geoffj
 
Would be better on the horizontal part I'd say. Pumping an open vented water supply is always going to be problematic to get right as air can easily get in. Most secondary circulation circuits are done on unvented hot water cylinders where none can enter.
 
Thanks - St0rmer66.

Do you suggest taking the vent off the tank. The plumbing is such that it "should" work.

I originally had no vent when the tank went in. This was OK until the heating element melted its solder joint as a bubble had formed at the top of the tank.

If there is a way to assure that the heating element will be OK, then the vent could be removed?

regards
Geoff
 
Thanks - St0rmer66.

Do you suggest taking the vent off the tank. The plumbing is such that it "should" work.

I originally had no vent when the tank went in. This was OK until the heating element melted its solder joint as a bubble had formed at the top of the tank.

If there is a way to assure that the heating element will be OK, then the vent could be removed?

regards
Geoff
Absolutely not! :!:. You could create a very dangerous situation if the cold feed valve was off/blocked you could at best split the cylinder or at worst make it explode! The vent pipe is critical.

Unvented cylinders are stronger and have various safety temperature and pressure related devices to stop such a thing happening.
 

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