Thermal Expansion Tank question

[Avgust]

Hi all,

I recently moved into a new house (built in 2016). I found a thermal expansion tank in an attic space above the garage. The valve to the tank is closed (see pic below). Shouldn't it be open?

Not sure if it matters, but the house has tankless gas heater.

Thanks in advance!

Alex

 

[Terry]

The expansion tank only works if that valve is open. They also don't last forever, so it's nice that they have a drain pan for it. I would check with your tankless instructions to see if it's needed. I guess so far it hasn't been. It's mainly for the volume of water in a tank that is heated. Most tankless are pass through heating.

 

[Sponsor]

 

[Avgust]

Terry,

I got RINNAI RL94i tankless heater. The instructions say "If a water heater is installed in a closed water supply system, such as one having a backflow preventer in the cold water supply line [which is what I have], means shall be provided to control thermal expansion.". I guess it means that the expansion tank should be there.

So should I go ahead an just open the valve to the expansion tank? Is there anything I should check before doing that?

Thanks!!!

 

[Jadnashua]

You should open the valve to it, shut the main water off, open a hot water faucet, then check the air pressure in the expansion tank (ET). That should be set to the normal pressure in the house. THat assumes you have a gauge and can check it, both the air and water.

If once you open the valve to the ET, then check the air pressure, it should be the same as your supply pressure. You could use that method as an alternative to buying a water pressure gauge to check. IF you get water out of the tank, or you tap on it and find that it is full of water, it's probably shot and needs to be replaced.

You may not have a closed system. Many water utilities DO install check valves that will make it one, though, and if there isn't one there now, it may show up as they do maintenance unannounced later. A pressure reduction valve will also make your system 'closed'.

If your system is closed, while since there isn't a tank per se, the hot water will still expand some but most of it just flows out the faucet during use. WHat's left can slightly stress things, probably more because it contracts as it cools off, but it's hard to say for sure. Regardless, the volume will be changing and if it can't go somewhere, puts stress on things.

 

[hj]

Normally, there is no 'expansion", unless the heater can operate without an open faucet, (such as having a recirculation system).

 

[Avgust]

Thank you all for your replies