thermostatic mixing valve madness

[tbxr]

Hi all

had some new horne 15 tmvs fitted which were set and left on 41 c but for some reason the temperature will not hold within +/- 1c. The temperature always raises up to 43-44~ after adjusting back to 41 with allen key. I have adjusted the tmv back to 41 for a few days in a row and the temperature holds while testing but when i come back the next day this is not the case. This is happening on quite a few new tmvs throughout the property (5 story building)

Is there any explanation for this or anything I can do except from setting them well below the 41c requirement?

many thanks

 

[Ch4 plumbing]

Check the strainers and if needed clean.
Are the hot/cold pressures balanced? If they are wildly different this can cause problems.
Is this a house or commercial property? If the later make sure you have fitted tmv 3 valves.