Need help with water expansion tank problems

[jkellar]

I was hoping someone could offer me some advice. I have a propane wall mounted heating unit. It has a one gallon(or so) water expansion tank built into the unit. I also have a 2 gallon water expansion tank installed and attached to my indirect hot water tank. The other day I was bleeding my baseboard heating pipes and I think I let the pressure in the pipes get too high causing a slow drip from the water expansion tank in my wall mounted heating unit. My questions are: 1) Do I need to replace the tank in my wall mounted heating unit or will the water expansion tank attached to my indirect hot water tank be sufficient? Can I just cap off the pipe to stop the leak? 2) If I need to replace the water expansion tank do I need to replace with the exact same one? They no longer make my "Fais" brand units? Can I replace it with a 2 gallon talk using flexible copper piping and house the replacement tank outside of the unit? 3)Can I fix this myself or should I call a plumber. I feel I am pretty handy.

The unit was built in 1990 by F.A.I.S. in France. Model # AR-820

Any advice is appreciated. Thanks, Jeff from VT.

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[Bob NH]

It isn't altogether clear but it appears that the red tank is leaking from the seam. If that it the case, it has failed and must be replaced before you have a flood.

You should be able to replace it with any similar size tank. If you are lucky, the threads won't be metric and you will be able to use standard US fittings.

A flexible connection will be OK if it is designed for the temperature and pressure. The flow is very small into those tanks so even a 3/8" OD copper tube would be large enough.

I would find a better way to support it than that tank supported by the plastic tank. You might be able to hang it between a pair of exposed joists.

You must be sure that the tank is designed for the pressure in the system. There are two classes of tanks: (1) Tanks for expansion in low pressure boiler systems, around 30 psi max, and (2) Tanks for expansion in sealed water supply systems (at least 75 psi).

If you put a low pressure tank in a high pressure application you could get a nasty failure. I remember an exchange on this forum where someone described the result of that.