Shower goes from cold to hot and repeats, not cartridge, not temperature valve

[khopkins]

Hi,

We moved into a condo that was built in the 80's in CA. The shower starts off normal temp, then goes cold, then gets scalding hot, and repeats back and forth every minute or so.

The owners say they had this problem before but changing the cartridge fixed it. We had the plumber change the cartridge. Didn't fix it. He tried a brass cartridge instead (of plastic) next--didn't fix it.

They installed a temperature control valve last night. Didn't fix it--now it actually seems to get even colder on its drop peak.

Any suggestions please!? This is terrible! We've been dealing with this for 2 weeks!

Thanks

Kim

[khopkins]

A couple more details-- we are the unit closest to the boiler. They have checked the boiler and say it seems to be working properly.

Other units have had this problem but the cartridge fixed it.

Our other faucets and showers in the unit have the same problem.

[phishfood]

Does the pressure change when the temperature changes? I am wondering if the recirculating pump is acting up. Just a wild guess, though.

[khopkins]

No the pressure remains perfectly constant.

A couple other important updates: The condo building uses a tankless water heater. We timed it with the shower yesterday. Every time the water heater turns on outside (about every minute), 30 seconds later our shower (and all the other faucets in our unit) gets a surge of incredibly hot water. Then it goes away, then repeats.

Is this normal for a tankless water heater to surge on and off like that? Shouldn't there be something that regulates the temperature going from the water heater into our faucets?

The plumbers want to now attach an 80 gallon water tank to the heater. Do you think that will work?

Please help, we haven't had a good shower for 2.5 weeks now!

[Chris]

Bump.... I would like to know the answer to this as well.^^^

[Malcolm]

Whats the "make" of the shower?

[havasu]

Tankless water heaters without a recirculating pump will have surges of hot water, warm water, then again hot water in various surges until the water in the pipes heats to a specific temperature. The closer you are to the TWH, the surges in temperature would be more noticable. By adding pre-warmed water before the TWH, the surges would be less noticeable, and may eliminate them completely.

I believe your plumber is on the right track, and it should solve your problem. Please let us all know the outcome after the installation of the water tank.