Read registers are float32 but write registers are uint16. Why?

This is the Hargassner design choice. Reads report precise measured values with decimals, writes accept only integer setpoints. The template scales writes appropriately so you can enter target temperatures in degrees Celsius without thinking about the encoding.

Buffer tank top reads higher than the boiler. Is that a wiring mistake?

Not necessarily. If the boiler just finished a burn and entered clean-out, the buffer tank may briefly read hotter than the quickly cooling boiler. Persistent wrong ordering suggests a sensor swap, but a few minutes of inversion around a firing cycle is normal.

Free Modbus template: Hargassner Heizkesselsteuerung

Name: Hargassner Heizkesselsteuerung
Brand: Hargassner
SKU: ac8742af-a98e-4201-b8d6-1f3e209526d8

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Free Modbus template: Hargassner Heizkesselsteuerung | ModbusCloud

Registers (27)

21 read / 6 write

Name	Address	Function	Type	Unit	Access
Outside Temperature	6201	FC03	float32	°C	R
Boiler Temperature A	6019	FC03	float32	°C	R
Boiler Temperature	6099	FC03	float32	°C	R
Actual Flow Temperature HK1	5999	FC03	float32	°C	R
Actual Flow Temperature HK2	6001	FC03	float32	°C	R
Actual Flow Temperature HKA	6011	FC03	float32	°C	R
Status HK1	6525	FC03	float32		R
Status HK2	6527	FC03	float32		R
Status HKA	6537	FC03	float32		R
Status Boiler	6511	FC03	float32		R
Buffer Temperature Middle	6151	FC03	float32	°C	R
Status Boiler A	6545	FC03	float32		R
Status Buffer	6519	FC03	float32		R
Control Status	6499	FC03	float32		R
Boiler Temperature 1	6013	FC03	float32	°C	R
Buffer Temperatur Bottom	6153	FC03	float32	°C	R
Buffer Temperatur Top	6149	FC03	float32	°C	R
Boiler Output	6513	FC03	float32	%	R
Consumption	6515	FC03	float32		R
Storage Volume	6517	FC03	float32		R
Status Boiler 1	6539	FC03	float32		R
Target Temperature Boiler A	7012	FC16	uint16	°C	W
Target Flow HK1	6999	FC16	uint16		W
Target Flow HK2	7000	FC16	uint16		W
Target Flow HKA	7005	FC16	uint16		W
Target Temperature Boiler 1	7009	FC16	uint16	°C	W
Target Temperature Puffer	7019	FC16	uint16	°C	W