One shower won't get hot (symmons temptrol, domestic mixing valve)

[Nsherman2006]

Hi all,

I'm at my wit's end trying to solve a shower problem. I live in a 2 bathroom house in CT. Both bathrooms have symmons temptrol showers.

The house has an oil boiler with steam radiators and a tankless coil for hot water. There is a Honeywell am1 mixing valve after the coil

The upstairs shower works fine.

The downstairs shower had been gradually getting worse about providing hot water. I rented the house our for a year and the previous tenant would turn the heat on before getting in the shower so the temperature would stay hot. I moved back in and the showers were only hot when the heat was on, but they would at least be lukewarm the rest of the time. Now they are just cold.

First, I contacted symmons for a replacement spindle for the downstairs shower. Replaced the spindle, no improvement.

I then got a special spindle that was designed for tankless systems, still no improvement.

I replaced the hot and cold seats, no improvement.

I then tried to track down problems elsewhere, and found that the domestic hot water valve is stuck. I can't get scalding hot water out of any of the faucets, but I can get warm water out of all of them (the shower that won't get hot is plumbed between the bathroom and kitchen sinks, both of which get warm)

More curiosly, the shower will get hot for about 5 seconds when first turned on and then return to being cold.

Any thoughts on what to do to get hot water to the downstairs bathroom?

Thanks!

 

[WorthFlorida]

Not sure if you tried this but I have always troubleshoot problems by eliminating then isolating.

Turn off the both the hot and cold water lines to the washing machine and check if your problem continues. Start turning water off to all of the faucets and keep checking to see if the problem stops.
What happens when you have the faucet turned to hot water only? If it gets cold, turn off the cold water to the shower and check again. If it gets cold then the problem is not the shower faucet. If it stays hot then it's the faucet. Since you changes the spindle I doubt it's the faucet.