Boxxer 421 fresh water invading my waste tank help

North County

New Member
Oct 27, 2018
Real Name
Tom Robinson
here’s where the thermo valve is “via” pointed with the screw driver.


Randy Dockins
Premium VIP
Nov 12, 2008
Real Name
Randy Dockins
Business Location
United States
If you have a piece of clear plexiglas put it on the waste tank instead of the lid . If it starts dumping water for it heats up to 200° plus it's the thermal valve .
I have found a simple way to tell if it's the dema solenoid or not. If the solenoid is working you automatically know it's the thermal valve. When the machine is warmed up simply set the temp control to about 170 or 180 degrees and let the machine get hot. Then simply turn the temp dial above and below that temp and watch your pressure gauge. It will move about 100 psi up or down as you move the temp dial back and forth. That's because the solenoid is being activated properly. When you see the psi gauge drop it is because the solenoid just activated so you know it worked. If you don't see any movement you know something is up with the solenoid. If the solenoid is working next thing to check is the thermal valve.

It's a handy trick to know that's helped me numbers of times. I also routed the hose for my thermal valve to my fresh water tank so I can actually see if it's working properly or not and it doesn't waste near as much fresh water or fill the waste tank up nearly as fast. It's been a whole lot simpler to deal with like that. The way Hydramaster hooks them both up at the same place on the waste tank is confusing and not to mention it fills the waste tank much faster.
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