Rannai Tankless water heater

Dannie

Does any have experience flushing a Rannai water heater. When I flush my heaters with the proper pump and hoses the flow keeps slowing down to a trickle. I power off the unit before I start and follow all recommendations but the vinegar flow slows down to minimum amount of flow????? Anyone have this same problem???

Larry Weingarten

Hi, Can you give us a bit more detail on what steps you're taking? For example, are you removing the strainer at the inlet? I'm not sure if it would work with that heater, but reversing flow periodically could help dislodge an accumulation of scale, which may be the reason for the flow slowing.

Yours, Larry

Dannie

HI Larry, I have had three sets of Rannai heaters over the years so I am not new to flushing them. This issue has been an ongoing one. I start by isolating the heaters with the isolating valves as the bottom of the heaters, clean the screen. I attach the pump in a bucket with vinegar to the inlet side and connect the outbound water valve which goes to the bucket. I have watched various videos some unplug the heater some just turn the heater off with the on/off button. I unplug it and the vinegar starts flowing but just wind up flowing at a very slow rate. Cannot figure out why, I have tried back flowing it same, I have tried unplugging the heater and just turning it off with the on/off switch same results. For a test I took off the inbound (connected to pump) hose leaving the outbound hose in the bucket. Turned on the street supply of water and it runs through strong and fast. The videos I have watched always show a strong flow but I cannot figure out why I cant get it to flow properly.

Thanks
Dannie

Larry Weingarten

Hi, I've two thoughts based on what you say. First, can you leave the screen out entirely when you do the flush? Second, what sort of pump are you using and how much higher than the vinegar is it? I'm looking for ways air could be getting involved and slowing flow from the pump.
Unless you're using a positive displacement pump, it will produce far less pressure than is supplied from your water main, so any restriction will show up in a more pronounced way. If you can show us a photo of the setup, that would help.

Yours, Larry

Dannie

Hi Larry, taking the screen might sound like a good idea however that would not explain why when I introduce street fresh water it runs strong. Second question I am using a submersible no air leaks and when I just use the pump and hose not connected to the heater pumps strong. I know it sounds like I am doing something stupid but for the life of me I cannot figure this one out.

Thanks
Dannie

hcpatel78

The pump pressure is either too high or too low.. There is water flow servo can only open or close at certain pressure. make sure you are not flushing higher than normal pressure .

Jamie Hall

Most likely, if using just an inexpensive submersible pump -- such as might be sold to pump out a basement of something of the sort -- you simply don't have enough head developed by the pump. Tankless water heaters have remarkably high head loss -- it's inherent in the design, not a fault -- and the typical one of two stage pumps simply can't put out much water. You need a pump capable of at least 30 psi -- 60 feet -- of head to do much of anything.

Dannie

Thanks for all your help in simple terms I see all the flushing kits have 1/8 HP pumps is that the right pump to use like one in these flushing Kits??
Thanks in Advance

Jamie Hall

I doubt very much that a 1/8 hp pump is going to push much through a tankless, but I can research that if you can give me a reference.