I have a 5 year old Takagi Tankles (TK1s) that has been operating well for the past years. In the past months we have been having intermittent problems of the water going cold while showering and filling a bath tub in 3 separate locations.

I don't see the problem with a standard hot only faucet on my sinks - just with our mixing valves in our Showers & Tubs. I am wondering if there is a problem with the Takagi now.

I have replaced the thermostatic cartridges in the bathrooms in question and it doesn't seem to be the solution.

So my question is what can I do - I can't always run into the utility room when it suddenly goes cold to see if the Takagi is running, and twisting the temp dial back and forth on my valves will usually cure the problem (minus the cold water sandwich).

My unit has never been serviced beyond cleaning the inlet screen, and flushing it out periodically. I do have hard water - so I would suspect that there is some scale build up, and it has never been de-scaled.

Thanks in advance.
Monty