Loosing hot water pressure in 3-5 seconds

[akintosyali]

Weird issue:
Water hooked up to the dock.
Cold water water pressure is great in all faucets.
for all faucets, hot water pressure drops from 100% to 50% (eye ball estimate) 3-5 seconds after turning the faucet on.

I took the filters at the end of the faucets, and the filters are clean.

I tried to follow the water line, there is one check valve on the pipe that allows the dock water in. If that was bad, the cold pressure should be dropping the same way, but cold pressure is good.

I went to my hot water tank. I loosened the drain nozzle and water came out in good pressure. I activated the highpressure check valve, and that also released water at good pressure.

What ever the issue is, it seems to be after the water heater, but before all the faucets.

I dont see any check valves between the hotwater out the faucets, but I I cant see the entire line either.

Can you you think of what else I should be looking for?

[bigbill]

maybe scale or some type of blockage coming out of the water heater

[Finalee]

maybe scale or some type of blockage coming out of the water heater

That's all I come up with.

[jim rosenthal]

Are these all hard lines or is there a flex hose sitting against something which might crimp it when it gets warm?

[akintosyali]

the water system is entirely on copper tubing. Only the 12V water system has reinforced clear hoses on it. I haven't checked the 12v system yet, maybe I will check that our too. Its a Kuuma. Do you know if it has an intenal filter??