Descale rinnai tankless water heater on right side of home Customer also stated the it seem to be circulating the water for Instant hot water but want to have it descaled first to see if that’s the issue I did look at circulating line and it hot at this time as if it has been circulating After getting customer approval I shut tankless down and flushed for 1 hour after flushing removed screen filter and cleaned as well then flushed tankless with clean water for 10 minutes after putting back in service turned water back on and circulating pump came on with no issues and ran until temperature was reached