After flushing the water run a long time before shutting off

The thermostat would not stop the heaters from getting hot . Is flush out the heater matrix make sure water flows nice and free . But I would be looking at the water pump and at the same time flush main radiator and heater matrix at the same time. The thermostat stuck shut will cause it to overheat but not stop the heat out of the blowers.

they get stopped up leave pressure on tank don't shut cutoff off hook up hose and run to outside then open drain valve with pressure on it for a min. it should flush.

there should be a screw adjustment on the ballcock or fill assembly...screw that down some to adjust...that regulates your tank water level....that screw goes in or out to adjust...one or other should do the trick...may have to do this a few times to get proper adjustment...good luck..

SOUND LIKE YOU NEED TO DRAIN AND FLUSH YOUR WATER HEATER TANK. THERE IS A HOSE BIB AT THE BOTTOM OF THE TANK. RUN A HOSE FROM IT TO A DRAIN OR OUTSIDE. SHUT OFF THE COLD WATER INLET VALVE AND OPEN THE HOSE BIB. OPEN HOT FIXTURES IN THE HOUSE.CHECK THE DRAINING WATER FOR CLARITY. IF CLEAR OPEN THE INLET VALVE AND LET IT FLUSH(YOU MAY GET MORE DISCOLORED WATER, RUN UNTIL CLEAR). SHUT HOT WATER FIXTURES, CLOSE THE HOSE BIB AND LET TANK REFILL.

It could be the type of flap you are using. I would suggest you try a different shaped flapper (a cone would work best) and if that doesn't do it, put a new kit into the unit, because it could be that the float system is sticking causing it to continue running.

One thing you might try is to shut off power or turn gas valve to pilot,as you didn't say if it was gas or electric. Hook up garden hose to drain valve and run hose to floor drain or sump basin. Shut off water supply valve to heater. Open drain valve and if you get a decent flow then let it drain tank about half way. If flow rate drops drastically then open hot side on faucet nearby to break vacumn.When you think tank is about halfway drained then shut off faucet if you opened one and close drain valve. Turn water supply valve back on and let tank refill. When it is full leave supply valve on and open drain valve and let water flush thru system for several mins. Close drain valve and run water on both hot and cold side of faucets fartherest away from heater as possible. Close this faucet
Turn tharmostat up as high as it will go and let heater run till it shuts off then return thermostat to original setting. Go through the drain and flush procedure a couple more times and this shold help break mineral deposits loose and flush them out. This should make for more efficeint operation and help prolong the tank life. Hope this helps you. Have a good new year and thank you.

Is the flapper dropping into place?

hi , replace your flapper on your flush valve assembly .
the link below is a spares dealer in the US
http://www.guillens.com/Toto/Flappers.htm

hope this helps
p.s. these parts do wear out

the right side where water comes to it through wall there is a cap that can be taken off it covers the shut off valve that takes a flat head screw diver to shut off or open up all the wall. check and make sue it is all the way open.

If it is shut it off and the cap on top where the flush handle is remove it once water is turned off and check it out. the kits to rebuild one it should be a 37-a or 36-a to replace this part if that is it.

These are a couple of thing's to check

sound like the water shut-off needs to be replaced.
if you turn on/off the shut-off, the tank get enough water to flush, then you get less water every time you use the toilet. that is the shut-off valve problem.
you may able to to just change the rubber seal.
I have not found change the seal will last as long as a new valve. better off, just change one.