I think I've found the answer:
Reading through the ZCL spec. thermostat cluster (0x0201), temperature attribute (0x000) and pi heating demand (0x0008) both have reporting access as mandatory. Looking in configurator, reporting tab of the thermostat cluster, local temp and pi heating demand are both enabled. 

I think I've found the answer:
Reading through the ZCL spec. thermostat cluster (0x0201), temperature attribute (0x000) and pi heating demand (0x0008) both have reporting access as mandatory. Looking in configurator, reporting tab of the thermostat cluster, local temp and pi heating demand are both enabled. 

If they re-appear if you  power off and on again, I think they are kept in simulated eeprom

That was something I considered, which is why I tried erasing the whole chip and re-programming.  

What do you mean “They are removed when I run the plugin commands”?

Sorry, that wasn't that clear. On the ZED, i can delete the reports using CLI commands:-

>plugin reporting print

00:ep 01 clus 0201 attr 0000 svr y report min 0001 max FFFE rpt-chg 00000000
01:ep 01 clus 0201 attr 0008 svr y report min 0001 max FFFE rpt-chg 00000000
02:
03:
04:
05:
06:

>plugin reporting clear 

>plugin reporting print

00:
01:
02:
03:
04:
05:
06:

I've created a sleepy end device and and router / coordinator using stack EmberZNet 6.6.1.0.
I'm using the reporting plugin.

Working through the CLI of the coordinator I've set up bindings and reports, and these appear to work

zdo bind 0xED27 1 1 0x0201 {086BD7FFFE016330} {000B57FFFEA788B9}

zcl global send-me-a-report 0x0201 0x0012 0x29 0 20 {00 00}
send 0xED27 0x01 0x01

However, I now have 2 reports on the ZED that I can not delete using the CLI command plugin reporting clear or plugin reporting remove n.

plugin reporting print (args)

 - Print the report table.
00:ep 01 clus 0201 attr 0000 svr y report min 0001 max FFFE rpt-chg 00000000
01:ep 01 clus 0201 attr 0008 svr y report min 0001 max FFFE rpt-chg 00000000

They are removed when I run the plugin commands, but re-appear if I power off and on again. 

I've tried erasing and re-programming both the end device and the coordinator, but this doesn't fix the problem (I was thinking that maybe the simulated eeprom may have become corrupt).

I am unsure how I got to this stage, but I can add and remove new reports, but I am always left with the above 2. 

Where am I going wrong?

I've created a sleepy end device and and router / coordinator using stack EmberZNet 6.6.1.0.
I'm using the reporting plugin.

Working through the CLI of the coordinator I've set up bindings and reports, and these appear to work

However, I now have 2 reports on the ZED that I can not delete using the CLI command plugin reporting clear or plugin reporting remove n.

plugin reporting print (args)

 - Print the report table.
00:ep 01 clus 0201 attr 0000 svr y report min 0001 max FFFE rpt-chg 00000000
01:ep 01 clus 0201 attr 0008 svr y report min 0001 max FFFE rpt-chg 00000000

They are removed when I run the commands, but re-appear if I power of and on again. 

I've tried erasing and re-programming both the end device and the coordinator, but this doesn't fix the problem.

I am unsure how I got to this stage, but I can add and remove new reports, but I am always left with the above 2. 

Where am I going wrong?

I've created a sleepy end device and and router / coordinator using stack EmberZNet 6.6.1.0.
I'm using the reporting plugin.

Working through the CLI of the coordinator I've set up bindings and reports, and these appear to work

However, I now have 2 reports on the ZED that I can not delete using the CLI command plugin reporting clear or plugin reporting remove n.

plugin reporting print (args)

 - Print the report table.
00:ep 01 clus 0201 attr 0000 svr y report min 0001 max FFFE rpt-chg 00000000
01:ep 01 clus 0201 attr 0008 svr y report min 0001 max FFFE rpt-chg 00000000

They are removed when I run the commands, but re-appear if I power of and on again. 

I've tried erasing and re-programming both the end device and the coordinator, but this doesn't fix the problem.

I am unsure how I got to this stage, but I can add and remove new reports, but I am always left with the above 2. 

Where am I going wrong?

The following is a screen shot of a question I am attempting to post, and the ask button does not respond.

There is some changes since EmberZnet 6.6.

Please refer to https://www.silabs.com/community/wireless/zigbee-and-thread/knowledge-base.entry.html/2019/05/30/migrating_projectsf-AsOr

unfortunately IAR extensions are enabled by default.

as far as I can tell, em_usb.h is included as follows:

#include "app/framework/include/af.h" ->
        "plugin/serial/serial.h" ->
        "com.h" ->
        "hal/micro/cortexm3/usb/em_usb.h"