How to Replace Expansion Tank

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Old 05-06-06, 06:23 AM
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How to Replace Expansion Tank

I have an oil-fired hot water baseboard heating system. The Extrol 30 expansion tank seems to be waterlogged (lately we hear a whistling sound when the boiler runs so something must be venting). The air vent on the air purger also has a lot of corrosion and some kind of white colored deposit on it. So I'd like to replace both of them. What do I need to do?

I assume I need to shut off the boiler and let it cool down. Then shut off the automatic water feeder and remove enough water so the system pressure drops to zero. Do I then just unscrew the old air vent and pressure tank and quickly replace them? Does it matter which one I do first? Then turn back on the automatic water feeder and then the boiler? I will use Teflon tape on the fittings. Is there anything else I need to do?

One other question. How soon do I need to do this? The system pressure is now 12 psi which seems normal. I will be going out of town for about a week. I'm reluctant to replace a few items the day before I leave. Can I let this go until I come back? Based on the weather forecast it doesn't look like there will be any need for heat in the week to come. Or is this pretty straightforward stuff that I easily replace without having to worry about some complication coming up? What is the risk of allowing the system to run with a waterlogged expansion tank?
 
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Old 05-07-06, 03:27 PM
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I assume I need to shut off the boiler and let it cool down. Then shut off the automatic water feeder and remove enough water so the system pressure drops to zero. Do I then just unscrew the old air vent and pressure tank and quickly replace them? Does it matter which one I do first? Then turn back on the automatic water feeder and then the boiler? I will use Teflon tape on the fittings. Is there anything else I need to do?
Pretty much the drill. You will most likely need to manually bleed air from your heaters in the living spaces.

I suggest that in addition to using Teflon tape that you also use a Teflon paste. Wrap 1-1/2 to 2 turns of tape on the fitting and then a light coating of the Teflon paste. Try not to have any Teflon tape on the first two threads as it will be cut off and may get into the system.

When cold your system should be at about 12 psi and when hot it will be higher. A defective bladder in the (or a waterlogged) expansion tank will cause the pressure to rise very quickly and release water from the safety valve.
 
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Old 05-07-06, 05:35 PM
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Expansion tank

If the relief valve has not been opening, I doubt the tank is bad.
 
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