Spluttering and spitting water from hot water tap

[Big John]

I've seen this too. It was a small leak at suction side of the pump introducing air. But I suspect the expansion vessel makes it seem worse by building up the pressure slightly higher than the pump delivers. (therefore hot at initially higher pressure than cold)

I am no expert but I would check your expansion tank. If you have had the system drained down the expansion tank depending on type empties out.
When you refill the system you should make sure the expansion tank does in fact take in a certain amount of water. There is a small bleed screw to allow the tank to fill half way with water. In my limited experience I have found if the expansion tank is not bled you get air from the tank mixing with the water flow which causes the spluttering. The spluttering increases with water temperature.

Expansion tanks are fitted in the hot water line which is why you do not get spluttering on the cold taps. It may be a long shot but worth a simple check. To double check short term - by pass the expansion tank as an experiment.

 

[pvb]

I am no expert but I would check your expansion tank. If you have had the system drained down the expansion tank depending on type empties out.
When you refill the system you should make sure the expansion tank does in fact take in a certain amount of water. There is a small bleed screw to allow the tank to fill half way with water.

I've never seen an expansion tank like that. Expansion tanks normally have a rubber diaphragm inside, with pressurised air on one side, and water on the other side. If the system is drained, the pressurised diaphragm moves to take up the space previously occupied by water. When the system is refilled and pressurised, water flows in to the expansion tank until the pressure is equalised on both sides of the diaphragm. There's no need to bleed air out (although it may be necessary to adjust the pre-charge pressure for best results).

 

[RichardS]

I've never seen an expansion tank like that. Expansion tanks normally have a rubber diaphragm inside, with pressurised air on one side, and water on the other side. If the system is drained, the pressurised diaphragm moves to take up the space previously occupied by water. When the system is refilled and pressurised, water flows in to the expansion tank until the pressure is equalised on both sides of the diaphragm. There's no need to bleed air out (although it may be necessary to adjust the pre-charge pressure for best results).

Indeed. As you say, in my experience, rather than bleed air out it's more usual to have to pump air in to correct any leakage.

Richard

 

[Minchsailor]

Expansion tanks are fitted in the hot water line which is why you do not get spluttering on the cold taps. It may be a long shot but worth a simple check. To double check short term - by pass the expansion tank as an experiment.

Are you sure? I have 2 expansion tanks, one is just after the pump (so supplying both hot and cold, the other (smaller) on the cold water supply to the calorifier. I added this second tank when I replaced the calorifier a couple of years ago - not sure if it has made much difference.

 

[vyv_cox]

Are you sure? I have 2 expansion tanks, one is just after the pump (so supplying both hot and cold, the other (smaller) on the cold water supply to the calorifier. I added this second tank when I replaced the calorifier a couple of years ago - not sure if it has made much difference.

The usual reason for adding a second accumulator after the calorifier is when a non-return valve is added to its cold water feed to prevent hot water from expanding back into the cold supply to the taps. If there is a long feed between the T where the cold water supplies divide this is not necessary, as the accumulator after the pump takes care of all of the expansion.

 

[VicS]

The usual reason for adding a second accumulator after the calorifier is when a non-return valve is added to its cold water feed to prevent hot water from expanding back into the cold supply to the taps. If there is a long feed between the T where the cold water supplies divide this is not necessary, as the accumulator after the pump takes care of all of the expansion.

Time to dust off this link again. http://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

Lots of peeps dont understand about accumulator tanks and expansion tanks. The link saves an awful lot of explaining