Burnham tankless hot water control

Leepoll

I have a Burnham Megasteam manufactured in 2007. I utilize the tankless water heater that used to serve the house without a problem. We can take long showers (20 minutes sometimes), but have a problem filling the tub for the kids bath (seems strange to me). I don't recall this being a problem until recently. I know I made a modification to the Aquastat at some point to try and save some money. I am not sure if there is a correlation to the low hot water quantity.



The system has an Honeywell Aquastat 4006a and a Honeywell AM-1 anti scald device. Is there a way to lengthen the time for the hot water to fill the tub? I thought the tankless was meant to be on demand- so to speak. What temperature setting should the Aquastat be set to? Wen I bought the house it was set to 160 and I reduced to 120. At the time- I didn't know how to adjust the AM-1.



Long question short... What's the magic or balance between the two devices?

Second question... Should I abandon this oil fired hot water and purchase a gas hot water heater?

Thanks in advance for the help.