How can we draw water out of an older-style traditional bladderless boiler expansion tank if water doesn't simply come out when we open the tank drain?
This article describes the steps in careful pump-assisted draining of a steel compression or expansion tank used on heating boilers. If this step is not taken when needed the waterlogged compression / expansion tank will cause boiler leaks and improper, even unsafe boiler operation.
In this article series we provide a heating system expansion tank / compression tank Troubleshooting & Repair Guide that will address just about any problem traced to this heating system component.
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Normally it's easy to drain a water-logged compression tank (expansion tank) on a hot water heating boiler by opening its drain valve.
If the proper plumbing fittings and controls are installed, draining the expansion tank and thus renewing its air-charge is straight-forward and should be done at annual boiler service.
That procedure is detailed at EXPANSION TANK DRAIN & AIR RE-CHARGE
But what can we do if someone has removed or modified the tank drain valve so that air can't enter the tank?
In that case the tank simply won't drain, and trying to cut open pipes or install an new, proper expansion tank drain can be both messy and expensive ,
Properly, opening the drain valve on a traditional steel bladderless heating expansion tank will let the tank's water drain out of the drain valve - because the drain valve is a special one that includes an air inlet that allows air to enter the expansion tank as water drains out, as we illustrate above.
But what if someone has removed the special tank drain and installed a simple traditional stop valve on the tank - without that air inlet? That's what we see below.
That's what happened to the expansion tank shown just below. This expansion tank serves a 1950s Weil-McLain gas boiler installed in a New York home.
During basement renovations a previous owner replaced the expansion tank with a simple copper elbow and horizontal drain line capped by a stop valve, thus permitting him to cover one end of the tank by a finished wall and ceiling.
The 1950's vintage Weil-McLain gas boiler worked OK for nearly seven years before its expansion tank became so water-logged that the new owners found that the tank needed to be drained.
Noticing that the gas boiler's relief valve was dripping and that boiler pressure was a bit higher than normal (boiler pressure should always be lower than the relief valve's opening pressure - i.e. less than 30 psi on a typical residential heating boiler), the owner realized that the probable issue was a water-logged expansion tank.
Watch out: while in this case it was natural to check and try to drain the expansion tank first, there are other causes of temperature/pressure relief valve leaks and some of them can mean that there is a dangerous situation.
See details at RELIEF VALVE LEAKS
The new owner opened the "expansion tank drain" but nothing happened. No air was able to enter the expansion tank - not enough to let the tank drain.
Worse, there was no easy to "fix" this improper installation without tearing down the finished wall and ceiling to regain access to the tank, and uglier still, simply removing the prior owner's plumbing would probably lead to a spill of nasty heating boiler water into the remodeled and "finished" part of the home.
We had success with this simple "fix" for drawing the water out of a water-logged expansion tank: we connected a small pony pump (Little Giant) between two washer hoses.
(An alternative that involves harder-to-rig-up parts might have been to combine an air inlet valve or schrader valve with a cap over the tank drain, more shut-offs, and a tee to allow using a source of compressed air to put some air into the expansion tank. In our OPINION that's a messy and dangerous solution that we don't recommend.)
To prepare for draining the expansion tank safely the owner:
Watch out: don't run the pony pump expansion-tank drain system continuously. You could damage the tank.
Particularly if the expansion tank is an old one that is badly rusted, perhaps rusted where you can't see the damage, there is risk that the tank might collapse, spilling that nasty heating water all over the place.
On one of our longer pump-suck-out cycles we heard a loud CLUNK! sound from the expansion tank. It may have simply been the now-lighter tank moving in its strapping up to the ceiling, or it could have been movement of the steel of the tank itself. Scary!
Taking care not to create too much vacuum in the expansion tank, we ran the pony pump just long enough to drain a couple of gallons out of the expansion tank and into that bucket shown on the floor below.
Then we stopped the pump by un-plugging it and, taking care to hold the down-end of the bottom washer hose out of water in the bucket, the vacuum created inside the expansion tank took a deep breath and we could hear the gurgling sound of air being sucked backup into the expansion tank.
We repeated this expansion tank pump-out cycle until, the "dink factor" approaching one, we allowed the tank to take one final deep breath of air.
Now it was time to return the boiler to operation
To understand the "dink factor" - the ratio of improvement to risk of a disaster -
see DINK FACTOR - Remembering Carol Schneirer
Watch out: using a pony pump to speed drain of a heating boiler itself can damage a bladder-type expansion tank too.
Those details are
at BOILER DRAIN DAMAGES EXPANSION TANK
The best repair for the boiler expansion tank shown above would be the re-installation of the proper type of tank drain, even if that means cutting an access opening in a finished ceiling.
But if the homeowner wanted to restore the proper original type of drain valve on this bladderless boiler expansion tank, she might have a devil of a time finding the proper valve to buy.
That's because most new hydronic heating systems use an expansion tank that uses an internal bladder and that never needs to be drained.
But the proper valve for these old steel expansion tanks still is available from heating and plumbing suppliers and from online vendors such as supplyhouse.com .
Shown here is the B&G Bell & GOssett DT-2 Drain-O-Tank Air Charger described by the manufacturer as:
DT-2 Drain-O-Tank Air Charger offers a sure, quick way to recharge a water-logged compression tank. The Working Pressure is 125 PSIG, and the Maximum Operating Temperature is 240F.
See this
...
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
On 2016-07-28 by (mod) - no water comes out of drain?
Darn I hate when that happens; I suspect that the tank is waterlogged but the drain is also clogged, perhaps with rust and sediment. OR the valve is a simple drain valve not a special valve designed for expansion tanks. The special valve allows air INTO the tank while water drains OUT so that the water can actually leave the tank.
You might need to replace the valve with the proper type (from your heating supplier).
But first try the procedure we show above on this page.
On 2016-07-28 by Danny jenks
What if tank is heavy and full of water but no water comes out of drain?
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