Tankless system goes cold periodically

[Venice230]

I have a tankless system. About once every four weeks, the system goes cold for 20 seconds. There is a temperature blend valve that looks corroded on the outside. I am guessing this may be the issue. Also, what is this valve called? Any suggestions would be appreciated.
Thanks

Rinnai system
RL75i
REU-VC2528FFUD-US (A)

 

[GReynolds929]

That looks like the old Microsoft screen saver, did the guy charge by the elbow?
That TMV looks like it's had a slow leak for a while, I would definitely replace it. I would have recommended replacing or removing it when the water heater was changed. I think they're pointless on a tankless and cause nothing but problems, but they're required by code in some areas.