Renewing inhibitor in underfloor heating system.

[cheddarman]

We have a Daikin Air Source heat pump feeding our hot water and under-floor 8 port manifold heating system.

The Daikin has just had its annual service and the engineer commented that the water looked discoloured and that the inhibitor needed replacing??

Is this an easy procedure? I'm pretty savvy at DIY so is it something I could do myself?

I've tried to find a local plumber but seems they're not interested (too small a job??)

Thanks