Tankless Heat Exchanger

If a tankless is descaled as the manufacturer recommends, you should hopefully not have to replace the heat exchanger. However, tankless heat exchanger replacements are sometimes necessary. This will not be a how to, because a heat exchanger replacement for a tankless should only be done by an experienced plumber with training specific to the tankless being worked on. Instead, this will be a broad overview of the process.

Remove Cover

The four screws – two on the top and two on the bottom, hold the front cover on the tankless. Removing this will let us see all the inner workings.

Take Pictures, Stay Organized

The plumbers will be sure to take a lot of pictures. These pictures are crucial when it’s time to put everything back together. In my personal experience, you can’t take too many pictures. I will feel like I’m being excessive when I’m taking it apart, but when putting it back together, I’ll always wish there was a specific close up or angle that I hadn’t taken.

The plumbers will also be sure to stay organized with each screw and disconnect. Different connections have different screws. Using a specific screw in the wrong place can cause leaks, so it’s important to mark each screw’s location!

Follow Instructions

The most important part of any tankless repair is to follow the manufacturer’s instructions to a T. This is especially true for a heat exchanger replacement. The manufacturer specifies what screws, disconnects, and cable ties to disconnect. They also send the specific gaskets, o rings, and parts to replace in the process of the heat exchanger replacement. The plumbers should be familiar with each part they disconnect, and why they must disconnect it. If the plumbers disconnect something that was supposed to remain intact, they will not have the proper gaskets to put it back together, and this can cause a water, gas, or exhaust leak.

Pull the Heat Exchanger

Before pulling out the heat exchanger, the plumbers will verify that nothing will get in the way of the pull. Often times, there’s a hidden wire or drain tube that needs to be disconnected, and its much easier to disconnect this before you’re holding a 30 lb heat exchanger. When it’s time to pull, the last 2 screws holding the heat exchanger are usually on the very back of the box, so the plumbers will need an extra long screwdriver (preferably magnetized) in order to reach them! On condensating units, the dual heat exchangers and the burner assembly will usually be pulled out all at once.


Most of the time, these heat exchangers will still be under warranty, and the manufacturer will only send out the warranty part. This requires further disassembly of the dual heat exchangers and the burner assembly.

Assemble, Test, Test, Test

Reassemble according to manufacturers instructions. The plumbers will be precise with all connection, especially the heat exchanger gaskets. Reassembly should be quick and easy for the plumbers if they set themselves up for success while disassembling.

After reassembling, the plumbers will test everything thoroughly. Test for power, test that the water gets hot and stays hot. Test for water leaks, gas leaks, exhaust leaks, and condensation leaks. Even if everything is done correctly, there can still be issues. Most of these issues can be addressed and solved immediately. Sometimes, especially on older units, the connections just don’t line up properly with the new parts. It is critical to call the manufacturer immediately once this occurs, and explain what’s going on. I have had manufacturers approve and supply a new, updated tankless unit in this situation, but they often require pictures, a video chat, and a thorough explanation of work performed. If someone unqualified to make tankless repairs did the work, the manufacturer will assume they did something wrong, and void the warranty.

Enjoy Your Hot Water!

Although tankless water heaters are awesome, top of the line technology, the repairs can be incredibly frustrating. If your plumber makes a manufacture specified repair, and it doesn’t solve the issue, I can assure you that he is just as frustrated as you are. An experienced plumber that specializes in tankless water heater repairs can eliminate many – but not all – of these headaches. Once you get things up and running again, I’m sure you’ll enjoy that hot shower just a little bit more! For more information or to schedule an appointment with us, reach out to McShea Plumbing today!

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