Mould in header tank

[Yeletah]

I have a Morso with back boiler, leading to 2 radiators further down the boat, the furthest of which has a header tank attached. I decided to check the fluid level in the header tank in anticipation of the cold weather and discovered to my horror a layer of slimy mould sat on top.

This in itself is relatively simple to get rid of - detach header from radiator and drain - but my concern is whether I should consider draining the entire system? Or is it likely that the mould has only occurred where the fluid is exposed to the air (there are a couple of small unused optional inlet/outlet holes in the tank)?

 

[Jen-in-Wellies]

Is the header tank (semi)transparent? The sort that is fitted to cars? If so, then light will have helped the mould, assuming it is green. Good news is that it will only be there as the inside of the rest of the system is dark . Would be worth draining the system, refilling and adding some inhibitor if it hasn't been done for a while to prevent corrosion inside.

Jen

[Yeletah]

It is indeed semi transparent so yes, that makes sense!

Thanks