Question about Water Flexcon WH8S Potable Heater Expansion Tank

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I have vented air out of my Heatslave 20/25 EXPANSION TANK

M y heating system shutdown , I discovered it had air in the system and vented every thing in sight including the expansion tank the system works very well at the moment when the system is off its 1.25bar when it is running at number 3 its at 2bar however I am worried that by venting the tank I have filled it with water and may have left no room for expansion.

Kind regards.

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  • Anonymous Mar 25, 2014

    The flexcon top expansion tank has no pressure after removing a radiator but cant adjust with valves



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Yes, you have let the air out of the expansion tank. You can not or should you have to vent an expansion tank. There is a rubber diaphram in the tank so just read the label on the tank for the proper psi/bar and put air in to that amount through the air valve. Problem solved.

Posted on Sep 13, 2009


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My boiler has a squeeling sound during the warmu up. I think it is coming from the expansion tank?

The squealing sound generally comes from a circulator pump, if it has a drive coupling between motor and impeller housing there is an oil cup/or oil hole, add oil until it is full! If it is a cartridge style circulator you may have to replace it.

Sometimes air in a system will cause this squeal noise as well. Purging the air out of system may be required. If you need to know how to purge a system there is a good pdf file at this link for $8.95 The Basics of Purging Air
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The Expansion tank is factory set to 12 psi and the only way to tell if it remains with 12 psi is to drop the system pressure to zero and check the tank with a pressure gauge. If water comes out the air valvestem when you apply the pressure gauge, the tank is bad, replace it! If there is less then 12 psi on the tank add air to 12 psi and open water valves back up to normal operating pressure. Usually the feed valve will automatically stop at the preset setting.If the boiler is leaking water out any relieve valve drains, the feed valve, relief valve and or expansion tank may need to be replaced.

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1 Answer

Therm-X-Guard Expansion Tank 2.5 Gal is leaking . can i take it off and repair it or cap the pipe that it is attached to

replace it. they dont cost much money. if you remove and cap it your pressure valve on the boiler will vent when it gets hot

Oct 27, 2017 | Water Heaters

1 Answer


Assuming this is not a steam boiler, your boiler probably has one or more of the following problems; (1) bad vent(s) not stopping after it purges air, (2) bad vent(s) that are blocked and can not purge air, (3) air bound caused by not inspecting #2 (and replenishing water, if needed) on a regular basis, (4) a water leak (low water cut off will prevent boiler from firing up), or (5) a defective supply water valve, or defective supply side check valve, or blocked water line, especially when sediment can easily foul the supply line. We need to look at the expansion tank. Is it water logged from a defective bladder? Is the Air Separator (near the X tank) operating properly? Similar to a vent, but larger, it can get clogged up and cause air to be trapped. Since the boiler will not start, you obviously have a low water condition. Solve that problem and you'll be warm again.

Feb 02, 2013 | Water Heaters

1 Answer

I have a Heatslave 12/14 oil-fired combi boiler installed approx 8 years ago. A problem has just developed on the domestic hot water side. My local heating engineer has investigated but so far hasn't...

Symptoms sound like crossover might be part of problem:
Crossover is when cold water enters hot water line due to faulty plumbing part like check valve, mixing valve, or bad faucet cartridge.

Jun 12, 2011 | Bosch Water Heaters

1 Answer

Hi, my halstead ace high boiler has started losing pressure and when i top it up to put the heating on after 10 mins the pressure is high whats wrong with it?

Probably a waterlogged expansion tank. The tank provides a springy air cushion for the water to push against as it expands, and the air pushes back as the water contracts. This scheme minimizes the pressure change that would otherwise be caused by expansion and contraction of the water, giving the water somplace to go when it expands. If the air cushion is gone ... big pressure swings.

Dec 28, 2009 | Water Heaters

1 Answer

Drained system to change cylinder. re-filled but heating will not come on now is it air lock

connect hose to expansion pipe and blow through with main pressure, blockage should blow back into your storage tank, best of luck

Sep 23, 2009 | Bosch & Power Vent Water Heater

1 Answer

Air in hot water lines only after installing thermal expansion tank. tank is mounted below water line .

Does you system have an auto air vent - has a cap like tire valve. cap should be left loose.

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1 Answer

Open vent central heating

yes it is possible toupgrade the system to a sealed one using a system boiler as you mentioned. the thing to bear in mind is to upgrade the radiator valves to pressure rated ones 10bar.
The probable cause of the over heating is down to the system being sludged up/cold feed blocked, or possible pump circulating problem?
I would recommend the installation of a magna clean filter to help keep the new boiler clear from system debris.I would definately power flush the system, if the system is a twin two port valve system then a automatic bypass should be fitted, all of this done by a corgi registered gas engineer



Dec 18, 2008 | Protech Systems FasNSeal FSWMKE4 4" Vent...

1 Answer

No heat in the radiators in the upstairs of our home.

Hi, What your looking for is called a (hy-vent). it bleeds air out of a system. you should have one on the top of your expansion tank. it is 1-1/2" in diameter and about 3" long. there is a little cap on top, unscrew the cap off. it looks like a bicycle tire valve. press the stem down inside until water comes out, then put the cap back on leave the cap loose so the hy-vent can do its job. it should be a self bleeder.

If this doesn’t work for you, please write back. Thanks,

Nov 19, 2008 | Water Heaters

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