Hi
I have a Hardie Dux HDE250 electric ho****er system, 250L. installed
1993.
I have had no problems with it except the the Pressure reducing valve was
leaking water so I replaced it. The hot water system accepted max of 680kpa
input pressure, the old valve was 0.53l/s at 700kpa, the new valve is
0.50l/s at 500kpa. A plumber who sold me the pressure reducing valve told
me the old one was too high(700kpa), and said 500kpa was better for my
ho****er inlet.
Fine, I replaced it, no more leaking water, but now I have a few more
problems since I did this. First night I took a shower the hot water ran
out after 2-5mins and took a long time to recover. I then tried again the
next day, then it was fine, no problems for 2-3weeks.
Till last night, the Temperature Pressure Relief Valve (TPR valve) that
goes from heater to drain was making a constant hissing noise all night and
the Discharge Tube was hot. I got up the next day to take a shower and the
hot water only lasted for 2-5mins and took a long time to recover.

Is he TPR valve stuffed? Are they expensive? The Pressure reducing valve
cost me $65 (AU).
The Discharge Tube is "always very hot" even when the heater was working
fine , should this be the case?
If the TPR valve is stuffed, how do I replace it with out burring my self,
do I turn off the water mains and hot water power and drain the water from
the heater by opening the TPR valve till the pressure in the heater tank
goes down?
Could this be due to the change of the Pressure reducing valve?
I don't see anything on the heater were I can adjust the temperature of the
water.

thanks
caven