Hot Water Flow to Shower Issue

[Jeff Bailey]

When the shower is going, suddently there will be a very noticeable and cold reduction in water pressure and hot water. Obviously, the loss is from the hot side. No other showers/baths/or water used at the same time. In fact, it happens when the shower is used before anyone else.

The flow will cut back on after about 30 sec, but it won't be near as hot as when the shower started. Crazy. Need help

[cacher_chick]

You have a tankless water heater?

[Jeff Bailey]

You have a tankless water heater?

Reg. gas-fired HWH. About 4 Y/O

[cacher_chick]

Then the problem is likely to be the pressure/balancing/anti-scald valve inside the shower valve.

[hj]

You have a problem that needs someone there to check it while it is happening. You do not have enough information for us to make a diagnosis. If you have a circulation system, then a bad check valve would cause those symptoms, but turning on the hot water in a sink would change the water back to hot again. But this is only one possibility among many.

[Jeff Bailey]

Then the problem is likely to be the pressure/balancing/anti-scald valve inside the shower valve.

If this IS the prob, will it get worse? I can live w/this but if its gonna get worse, I pretty sure I'm gonna get it fixed over the holidays