In the springtime had installed Viesmann Vitronic 100 and Superstor 45 gallon indirect water heater. Shower is delta Carlisle rated at 2.5 + 2.5 GPM. Water heater on priority zone. Boiler has outdoor reset setback controls. Installed by very reputable contractor. Oil fired. WH was set to 130 and boiler temp varies.
First shower of 20 minutes with flow throttled back approx 60-70% of max flow and runs out of hot water and have to turn temperature ALL the way up. No other loads on DHW.
Had NONE of these issues during the summer months, plenty of hot water. Now the boiler is running for heat we have the shower problem. Had shower temp set in the middle at all times no matter how long the shower.
I was assured this set up would supply plenty of water unless really hot and really long showers back to back.
The contractor came by and made some adjustments with little or no change in performance.
Any ideas what to discuss with installer? This is not much better performance than I had with a 20 year old tankless POS.