Boxxer 318 heat or lack thereof


Randy Dockins
Premium VIP
Nov 12, 2008
Real Name
Randy Dockins
Business Location
United States
My brand new Boxxer 318 is driving me crazy. Works great except heat. Was getting about 100 degrees (50 ft. of hose at 400 psi, 6 flow). The tech guy at my dealer told me about adjusting the screw behind the temperature select.

The selector was clicking at about 10-11 o'clock on the dial, so the tech told me to turn the screw behind the selector counter-clockwise a quarter to a half turn, until "the click" started happening at 7-8 o'clock on the dial.

Did that and now I'm getting around 145 degrees, but the screw on the back keeps moving clockwise back to its normal spot, sort of like the vibration of the machine running at full-blast make it move clockwise. I can hot glue that in-place but it didn't totally fix the heat problem.

Even with the heat on max. and my wand spraying, there is still water being diverted to my waste tank, even with my piddly 145-150 degrees. Not as much as before adjusting the temperature selector screw but still quite a bit.

When doing the test, the machine is at full throttle, the intake to the tank is blocked, the vacuum is running at 14 hg, pump at 400 psi.

When I move the temperature select dial and it clicks, my water pressure instantly increases about 80 psi. Not sure what that means.

Anyway, the machine only has 6 hours on it, so I'd appreciate any help. Hydramaster is telling me I'm expecting too much from the machine, as if 145 is good at low pressure and flow.

Thanks in advance if you have time to help.

I doubt you will fix this yourself. Sounds like you have some kind of problem with the temp control on the machine. It sounds like your high-pressure solenoid is dumping way too much water and that's why you're not getting any heat. The water that it's dumping is your heated water so it's going right into your waste tank. That shouldn't be happening hardly at all if you're setting the temp dial to max. The reason why you see that large pressure variation is because the solenoid just kicked in and all of your heated water just went bye-bye. This is the water that is AFTER the heat exchange. If the machine were working properly you could set that dial anywhere you want it and the machine should maintain that temp pretty close. It mainly does that by opening and closing the solenoid. By setting it to max it definitely should hardly dump any water, perhaps none, while you're wanding. I have always set my machine to max for carpet cleaning to prevent excess dumping and to maintain my heat better.

I suspect you will have to take this in for warranty service which will cost you some time, but they shouldn't be charging anything otherwise. I would not attempt to make any changes or modifications to the machine under warranty. Btw, your machine is probably only rated for a 4 flow wand and you won't get quite as high of temps with a 6 flow, but it definitely should be a lot better than what you're getting. I have two wands for my Boxxer 421. One is a two jet 4 flow and the other a 5 jet 7.5 flow. Obviously, I can maintain higher heat with the 4 flow, but most of the time that really doesn't make that much difference so I think you're fine with your 6 flow.

Btw, the fact that you do have a pressure variation tells me most likely the high-pressure solenoid is functioning right. If you didn't see that variation when you turn the knob you have a problem with the solenoid so that is actually normal. Your problem seems to be with the component that controls your temperature which includes your solenoid and your diverter. That solenoid is called a normally closed solenoid. The temp control activates it and causes it to open to keep your temp setting or to prevent the machine from overheating.
Last edited:


Active Member
Jul 31, 2012
Real Name
Edward Arnold
Business Location
United States
Unless they have changed the way things work on the unit. There is a sensor that is called a RTD sensor that is what works between the thermostat and the computer board to control the bypass system. If it is bad it will cause it to bypass to soon. It usually has a white outer cover with two wires inside. If you take the lid off of the fuse panel you should be able to see it and follow it back to where it is in the unit.

Chris Kelley

Active Member
Apr 19, 2017
Real Name
Christopher Kelley
Thanks everyone. Does the fact that turning the screw behind the temperature selector increases heat mean anything?

Bought from a distributor in Tampa and I’m in Dayton, Ohio. There are HM dealers around here but they sure don’t want to take care of me since I didn’t spend 3k more to buy the unit from them.