In a word, nope.

If the expansion tank is located at the cold water service line to the WH and the softener is installed at the water service entry to the house there should be no problem caused.

Was the softener installed at the water service entrance or is it only softening the water heater?

Couple things to check...

Is the softener running water through the drain line to the drain constantly?

Is the water flow indicator flashing even when water is not being used?

Are you absolutely sure the softener is plumbed correctly and not BACKWARDS?

You'd be better off to make sure the thermal expansion tank isn't waterlogged and has proper air pressure and put it back in service and bypass the softener till you figure this out.

Thermal expansion tanks are passive devices. You should drain the tank and check that the air charge is correct, but that won't cause the problem you're asking about.

With a closed plumbing system without the thermal expansion tank operating properly and connected you run the risk of damage to your water heater, plumbing fixtures, appliances, and plumbing.

After reading a little more about expansion tanks and such, I promptly ignored his advice to bypass it and re-opened the valve.

Here's a few answers to some of the questions above:

Softener is installed at the water service entry for the whole house and the expansion tank is installed at the cold water service line to the water heater.

Softener does not appear to be running water through the drain line constantly.

The flow indicator does not appear to be flashing even though no water is being used.

I am pretty sure the softener is plumbed correctly, as long as the untreated water coming from the main should be attached to the valve side with the arrow pointing in to the control panel and the plumbing taking the water back to the house supply line is attached to the side of the valve that has the arrow pointing away from the valve or towards the wall if you will.

One thing to note is that the plumber decided to put a check valve in on the line exiting the softener approx. 8" up from where the water line exits the bypass valve. Could this have anything to do with it?

It's impossible to tell what's going on now as the meter had run down to about 359 gallons remaining til regeneration and it appears to have gone in to countdown mode to a 2:00 AM regeneration. I'm guessing this means that it is going to regenerate tonight based on the fact that 359 gallons would not possibly get us through another day based on the usage numbers that have been logged on the meter in the past 30 hours (1100 gal.) since it was installed.

I guess I will have to keep an eye on it tomorrow, but I can't have this thing regenerating every 2 days.

"One thing to note is that the plumber decided to put a check valve in on the line exiting the softener approx. 8" up from where the water line exits the bypass valve. Could this have anything to do with it?

Yup... could be restricting the flow and creating back pressure driving the turbine wheel in the control valve nuts.

Get that check valve out of the line and bypass the softener until you do.

Next time you're contemplating water treatment call a water treatment professional and not a plumber.

You should also install a three ball valve bypass in the plumbing along with the Clack bypass. That way, if the Clack bypass fails or leaks you'll still be able to have water, albeit untreated, to the house while you're waiting for parts to arrive.

The check valve is out of here ASAP, but I also thing I found the source of the problem. Found a toilet that was running wide open the majority of the time. I didn't find it when I checked last night or by watching the meter, but my wife noticed it when she was up feeding the baby.

Here's the best part, I think the reason the toilet was running was because the plumber open the regulator to increase the water pressure to the entire house. The increased pressure while filling the toilet tank made it harder for the float to shut off the water. The contractors also did a crummy job installing the float and it looked like it was dragging on the tank wall, so that didn't help either.

I will keep an eye on it and make sure, but it appears that we may have isolated and fixed the problem. In the meantime, I am going to have the plumber take out the check valve and return our water pressure to where it was. Thanks for the advice and help.

Drew

Good catch on the toilet and the bad plumber.

The flow indicator ("softening" on the upper LH corner of the display) on the Clack should have been indicating (flashing) that water was flowing through the softener but if it's a low flow the indicator won't flash.

Set the static pressure in the house at 60-70 psi and check all the toilets flappers you have.

Fixing the running toilet fixed the usage problem and the softener appears to be functioning perfect, which I guess begs the question, is it OK to leave the check valve in? It does not appear to be restricting flow in any way (valve shows maximum SFR to date of 13.9 gpm) and I don't think it is creating any back pressure.

Wouldn't the check valve actually prevent any back pressure from reaching the valve and resin tank and in turn protect the resin tank and valve?

Say for instance that the expansion tank was malfunctioning for whatever reason, and the water heater kicked on and created a brief expansion that drove the psi up to say 150 psi and that back pressure pulse was pushed back to the check valve since the expansion tank didn't work correctly. Wouldn't the check valve slam shut and prevent this back pressure from reaching the resin tank and valve?

If the normal line pressure on either side of the check valve is the ambient 60-70 psi of the system under normal conditions and a back pressure pulse of 150 psi comes from the water heater side of the installation, isn't that precisely the set of conditions that would cause the check valve to close and keep the pulse on the water heater side of the system?

I realize that with check valve in place and the theoretical malfunctioning of the expansion tank, the pressure pulse will seek some method of escaping which could cause damage somewhere in the house like a faucet or toilet, but at least it will not have blown the resin tank or destroyed the control valve, correct?

I hope this rationalization makes sense, but I'm not sure that I have done a very good job of positing my questions or explaining the scenarios. Oh well. Take a swing at it if anyone feels like it. I am interested to hear some opinions on this one.

I'm thinking more potential bad will come from disassembling a functioning, dripless install than from keeping the check valve in place. Thanks.

Drew

We had the same problem after a new Rheem hot water tank was installed with an expansion tank on March 26. The water softener thought we were using 800+ gallons a day, so it began regens every 24 hours, sometimes more frequently. The relatively new PentAir water softener controls were adding up the gallons flowing back and forth in a cumulative manner -- versus substracting reverse flow like our city water meter does. That's how we isolated the problem -- our household usage (as viewed on our city's online monitoring dashboard) was showing no higher usage from leaky toilets, etc, only spikes whenever we had regens. And they began happening every night at 2 am, immediately after the new water tank was installed. This was during our current coronavirus quarantine, so we were having to have service people come in and out of the house --- it was stressful. We tried having a check valve installed just above the water tank supply pipe, but the valve was apparently faulty, and knocking in the pipes began. This happened regularly, and sometimes went on for 30 seconds at a time. It sounded like the whole house was going to explode -- not a comforting should to wake up to in the middle of the night. Our plumbing company came back a third time on April 16, and after discussion, we eliminated the check valve and expansion tank altogether. Just kept the new water heater. Now, no more noises. We realize this may reduce the life of the new water heater, but we're willing to take that expense vs. living in what sounded like an groaning old ship at sea.