Air Block in Hot water Solar system causing water pump to switch on and off.

[raybarrell]

I have a Solar hot water system which has an air vent fitted at the top of the panels ( not sure if it is working correctly?) But I have a problem with air in the hot water system causing the water pump to switch on and off continuously. I notice on the water pump gauge pressure decreases when water is switched to supply the house, which causes the pump to switch on. I have checked for leaks and is o.k. so I am sure it is a air block as also no hot water is reaching the taps. I think what is needed is a 'Automatic Hot Solar water Air vent?' Does anyone have any advice on this please? Also where one can buy such a vent in Pattaya Chonburi area Thx.

[jvs]

I would attach a water hose to the lowest end of the system and open the system at the top and let the water pressure blow the air out from the bottom up.

[Rimmer]

Moved to DIY forum for some more input on what can be the problem

[NeverSure]

I can't picture what you have. My thought is that maybe you don't have enough air in the system.

Are you aware of how a normal pressure tank on a well works? There is a tank with water in the bottom and air at the top? Since water can't be compressed but air can, the pump compresses the air until it shuts off from enough pressure. Then when you turn water on from the tank the air begins to decompress but not enough to turn the pump back on for a while. Then when the pump comes on it not only pumps in water but also recompresses that air until the pump shuts off.

The air is the buffer that keeps the pump from going off and on every time you open a faucet. My pump pressure switch is set to start the pump at 35 pounds of pressure and shut it off at 45 pounds. Thus the pump won't come on until enough water has withdrawn from the bottom of the tank to decompress the air to 35 pounds.

Another possibility is that your pressure switch that turns the pump on and off is set to too narrow of a band. They are usually adjustable. If there isn't enough difference in the "on" pressure and the "off" pressure the pump will go on and off quite rapidly.

Cheers.

[IMHO]

You'll know if the "air vent" on top is working, because you'll hear "woodpecker sounds" every now and then as it vents off hot gas.

I got the same issue you're describing when my main pump failed - the solution was just to open a hot water tap and wait for all the gas to escape - which took around 15 minutes.

I'm not sure if they're all designed the same, but my 2 solar hot water tanks (both pressurized types) are not designed to keep anything but water. As the water heats up, it generates gas, and that is vented off.

[fredge45]

Another thing to check is to make sure that any check valves in the system are working freely. Took me a while to run that one down - replaced the sticking valve and all is working fine now.