Red Expansion Tank - Air Source Heat Pumps (ASHPs)

RE: Red Expansion Tank

BobTSkutter — Sun, 23 Feb 2025 14:48:50 +0000

Excellent, I'm glad it's settled down.

Regards

Bob

RE: Red Expansion Tank

Richard24738 — Sun, 23 Feb 2025 13:17:10 +0000

@bobtskutter Hi Bob. Just a short update to say that the Red expansion tank guage is stable on 1.2 reinforcing my thought that it was air in system. It was drained down 4 weeks ago and maybe the release of trapped air was delayed or maybe I just hadn't noticed it.

I will still keep an eye on it though.

RE: Red Expansion Tank

BobTSkutter — Fri, 21 Feb 2025 19:38:17 +0000

:) I'd love to know what you find out, please post the solution.

Regards

Bob

RE: Red Expansion Tank

Richard24738 — Fri, 21 Feb 2025 19:07:22 +0000

@bobtskutter Hi Bob. Daft mistake with the valve.

The red expansion tank is not attached to the hot water cylinder.

I can't find the PSV you mention on the heating side.

Filling the system from 0 to 1.5 did not take long although I did slow it down towards the end. I'm only guessing maybe 5 seconds and then a few more.

The installer did ask me to check the auto air valve on top of the buffer tank to see if wet. Totally dry and always auto open so I don't know if it's been venting air. Maybe that's it!

A few weeks ago the system was drained down so maybe trapped air in the system has suddenly found it's way out. Hope that's the reason and why the pressure only dropped.

Will monitor the pressure over the weekend.

RE: Red Expansion Tank

BobTSkutter — Fri, 21 Feb 2025 18:27:44 +0000

OK, that is a pressure relief valve for your hot water cylinder, not your heating system. That valve is to protect the cylinder from bursting. There is another one somewhere for the central heating system.

Is the red expansion tank you checked attached to the hot water cylinder or to your central heating system. If you're unsure then getting the installer back to check things is a good idea.

You can loose pressure for several reasons.

The expansion vessel could have failed.

There could be air in the system that's being vented through an auto air vent, but loosing 1.5bar is a lot of air to "suddenly" vent from the system.

There's a water leak.

How long did it take to pressure the system from 0 to 1.5bar? Did you have the fill valve fully open or only slightly?

You've got the installer coming to look, that's good.

Regards

Bob

RE: Red Expansion Tank

Richard24738 — Fri, 21 Feb 2025 18:14:53 +0000

@bobtskutter Thanks. Pressure remains steady at 1.2 with the system idling after House Heating.

No idea what's trigering the drop in pressure.

I have attached a photo of a valve on the side of the Hot water tank. Is this what you are refering to?

10548

RE: Red Expansion Tank

BobTSkutter — Fri, 21 Feb 2025 17:42:07 +0000

The valve on top of the red expansion tank is what's used to fill the air bladder inside the tank. It's good that water didn't come out. The installer should check the pressure inside the bladder to make sure it's set properly. The proper value depends on how much water is inside the system, but it's typically about 1.5bar.

I've attached a pressure picture of a pressure relief valve, but the one you have might not look like this. It sounds as though you've found the outlet line and it's not wet, so that means the valve isn't leaking.

Please keep an eye on the system pressure, if it starts to get to 2.5 or 3 bar then I recommend you turn off the heat pump and wait until the installer has checked things.

Regards

Bob

10547

RE: Red Expansion Tank

Richard24738 — Fri, 21 Feb 2025 11:33:58 +0000

@bobtskutter Hi Bob. Installer asked me to check the pressure relief valve on the top of the Red Expansion tank. Only air came out; pressure was 1.5 and the pump was running. So, unfortunately maybe not the expansion tank.

I have topped up the water so the pressure is back up to 1.5.

Not sure what a PVR looks like. Does it vent to the outside? There is a pipe on the outside - no noticable water but maybe that only occurs when the pressure drops to zero?

Pump is idling in this mild weather and is still at 1.5 but I will keep an eye on it.

Installer will come early next week.

RE: Red Expansion Tank

Richard24738 — Thu, 20 Feb 2025 19:06:12 +0000

@bobtskutter Thanks. Chasing up my installer.

RE: Red Expansion Tank

BobTSkutter — Thu, 20 Feb 2025 18:57:43 +0000

No it shouldn't, the pressure should stay fixed at what ever you set it to - which is normally about 1.5bar. It should never go to zero and back up to 1.5bar when it gets warm.

Let me provide some back ground.

That red expansion tank contains a balloon filled with compressed air. If the air leaks out of the balloon because there's an AIR leak in the schraider valve on top of the cylinder, the pressure will suddenly drop very low. Which is what you described.

As the system warms up the water will expand and the pressure will rise, and go up higher than normal. You said it gets to 1.9bar. That means the pressure has increased by almost 2bar as it's warmed up - which is a lot. And that makes me think the air balloon (proper name is bladder) has depressured.

You can test the expansion vessel by opening the schraider valve cap (looks like a car tyre air valve) and see if water comes out, but I recommend you get a plumber to check it.

Also, if your system was operating at 1.5bar and then it went to zero that's quite a lot of water to leak out. Could be 1 or 2 liters depending on your system size. I'm pretty sure you'd notice 2 liters of water on the floor.

The other place water can leak without you knowing is via the pressure relief valve. It could be anywhere on your system, if you know where it is have a look at the outlet pipe from the valve, if it's wet then the pressure relief valve as failed.

Regards

Bob