I've got a Navien Combi 240a which is giving inconsistent and low domestic hot water out.

I do not have the remote but the LED on the unit shows supply temps which oscillate from 180 down to 150. I assume this is not the DHW output because the DHW output pipe is only warm to the touch.

The mixing loop for the hydronic heat, however, is scalding.

My understanding is that there is a valve inside which is supposed to switch the primary heat exchanger loop to the DHW heat exchanger when DHW is called for.

I am not calling for heat at all because it's august. My Taco controller is not showing either thermostat calling for heat and my heating loop pumps and valves are not running.

Last winter, on particularly cold days I had issues with a "low pressure on heating side" error, which hasn't happend in this summer.

Can anyone weigh in on these questions -

Is the three way valve sticking?

Did my installer jack up the install somehow when wiring the heating controller? The DHW was flawless before having the heating loop wired, but it has seemed to work well this summer.

Is there a setting to disable the heating mode entirely until I get this figured out?

Is anyone in Denver area an expert or know an expert on Naviens?

Thanks!