Hot water trickle

It sounds like a failed mixing valve, they seize up and will let a small amount of flow through that will build the pressure up past the valve but as soon as you open the faucet the pressure drops to what will flow through it. Don’t know if you have one but usually mounted on the hot outlet of the water heater.

As other have stated, the check valve has probably failed. This happened to my daughter, and at the time, I was unaware they had a check valve. A friend helped her replace it, and all was good.

The keeper or the spring deteriorates over time, and eventually the check valve checks "the other way"...

What kind of bypass valve system do you have 1,2 or 3 valve.

The reason I ask is with the one valve system there is a check valve, may be two. For sure on the Water Heater outlet (some have it on the inlet) from the sounds of your problem you have one on the inlet adn it's clogged. Or a pinched line on the line on the inlet side.

had this problem in my house when I had one. Finally replaced a piece of pipe that was seriously clogged .

Boon Docker wrote:
OP stated all 3 faucets.

Then it is the WH Tank HOT Out check valve

OP stated all 3 faucets.

At all faucets or just one?

How long ago did you replace the WH Tank Hot Out Check Valve?

You could have a blocked line, a valve not wide open, or maybe a kinked pipe. Looks like you have checked everything else that comes to mind.

Whether on city water or 12 volt pump the trickle is still there

When using on board water supply, turn on hot water, does pump turn on?

Check valves have been replaced and unit has never been winterized..