Hi- I have a 2001 Marquis Ultimate Series w/Ser.# SMUS361-0210028. Balboa Control Pack MTS1U. The temperature acts erratically. For the last few months I would set it for 102F and come out there and it will be 105F. Or, then will set it for 98F and sometimes I'll come outside later and it will be 102F. Lately when I've been in it, I set it at 103F and the temp keeps dropping even though the heater light is on and the pump is running. Checked fuses/connections and all looks to be in order. No corrosion anywhere. What could be the problem and what is the fix? Thanks for your help,

D. Chad Quilici
Seattle, WA

Well you're in Washington, so first thing I'd suspect is dropping temperature due to the spa cover being off when you're using it (in the cold weather).

Another consideration is if this spa is set up for 50 amp (or more) or 20/30 amp service, which will turn off the heater when any jets or blower activation occurs.

You didn't post your spa system power information so I've got to guess first.

It's on a 50amp setup from the main panel to a GFI box 6' away from the tub. It's not the cold Washington weather. I've had it a couple years and last year I'd sit in it in the middle of the winter- that being upper 30's/low 40's most days- and it would keep the heat up to whatever I set it at with no problem. If I set it to 103F and it would drop a degree, the heater would come on and heat it right back up one degree and kick off. Now, I set it at 103F, get in, it starts dropping, the heater and light comes on, but the temp just keeps dropping and it doesn't maintain the same heat level (even though it acts like it's heating) and then I have to get out.