Swimming Pool Blog

Gas Pool Heater Replacement

Installing a New Heater
by Rob Cox, May 17, 2012

Gas Pool Heater Replacement

 jandy legacy pool heater installation

Yesterday, I installed a new Laars Legacy natural gas pool heater with Myles McMorrow, president of Pool Services Network, at a pool in Falls Church, Virginia. We were replacing an older Laars Lite model, probably 15 years old.

What follows is our story of replacing an old pool heater. We detached plumbing, gas and electric, moved the old heater aside - and made new connections to our replacement heater.

Gas, Electric and Plumbing work can be dangerous in the wrong hands. Please be sure to contract with licensed and insured companies to do this work.

Chapter 1: The Demolition

This is the fun part. Starting with the pvc saw, we cut the pipes that are coming in and out of the existing heater. We chose a location that gave us at least 1.5" out of any fitting, to allow us room to connect the new pvc pipe to the old.

Next, we disconnected the gas line. We shut off the gas at the meter, and also closed the valve outside the heater, just before the regulator. To disconnect the old pipe to the new, we removed the heater's front door, and loosened the union connection on the incoming gas pipe. A pipe wrench allowed us to then remove both pipe pieces, the short nipple screwed into the gas valve, and the long one that met a 90 degree gas pipe fitting outside of the heater.

For the electrical, we had a 3/4" conduit sticking up out of the ground, that was running from the main time clock box / breaker panel. Inside the heater, we moved the controller assembly out of the way to access the wires as they entered the heater cabinet. Removed a lock nut on the conduit fitting, inside the heater, and then took off a few wire nuts and we could pull the incoming power wires out of the heater.

We had a very tight space to work in - not much room on either side of the heater, and a large bush that prevented an easy exit from the equipment pad. We didn't want to risk knocking into the gas line or breaking the electrical conduit that stuck up out of the ground, unsupported, so we decided to tear it down a bit. After removing the heater top and a few side panels, we could remove the heat exchanger. We set these items aside. This reduced the weight of the heater by about 60%, so we could more easily manage to move the old heater out of the area. 

After moving the old heater out of the way, we cleaned off the pad and cut the bushes back a bit. Heaters will last longer if they are not surrounded by bushes and overhanging trees, which trap moisture around the heater. The heater we removed had years of being hidden away from the sun, buried in what I call the Virginia jungle. This heater had so much rust, the bottom was completely gone.

Chapter 2: Plumbing In

The new Legacy pool heater has union connections that were packed inside of the heater. We installed these and made note of the markings on the inlet header, indicating which port was "In" and which was "Out". Usually, if you are installing the most recent version of the same manufacturer pool heater, the old and new heater line up perfectly, and you may not need any new plumbing at all. Just move the new heater a few inches closer to the pipe, to make up for the bit of pipe that you cut off. 

laars legacy inlet outlet ports are further apart than laars lite

In this case however, we were not so lucky. Turns out that the new inlet/outlet header on the Laars Legacy heater sits about the same height as the old Laars Lite, but the inlet and outlet are further apart from each other. Our pipes going in and out of the Laars Lite were within 1/2" of each other, but the Legacy needed to be about 2" apart.

This required us to cut further back, along the old pipe, and rebuild it with 2 - 45 fittings, a coupling, and a bit of 2" pvc pipe, so that the pipes would line up correctly. When plumbing pool and spa equipment, we dry test our connections first, then we use a clear pvc primer to soften and clean the pipe and fittings, just before we glue them together. 

Once we had reconnected the pipes to run in and out of the pool heater, our plumbing portion was complete. Next!

Chapter 3: Wiring Up

It would have been nice if the knockout in the heater cabinet was in the same location, but we didn't have that luxury. The new heater had a hole for the wiring to come in that was about 12" higher than the old Laars Lite location. Problem. Our conduit doesn't line up. 2 solutions were discussed - we could extend the conduit or we could drill a new hole in the cabinet. We like to use power tools, so we chose the second option and made our own "knock-out" to bring the power wires inside the heater.

wiring instructions for Laars Heaters

Once we had the wires running inside, we had to figure out if we were wiring the heater with 110 or 220 volts. We carefully used a test meter to check the power being supplied to the wires coming into the heater. Actually, we did this after we assumed that it was 220 volts, and then when the heater didn't start, we had to rewire a few things to get it connected properly.

New heaters, like new pool pumps, will come wired for 220V, to protect it from idiots like us. Laars provided very detailed instructions in the Legacy owner's manual, and on a tag attached to the wires inside the heater. We had to join a few wires together to allow the heater to accept 110V. With that done, we were getting "lights on the dashboard" so to speak, and our new heater wiring project was done. Next!

Chapter 4: Connect the Gas

We used the same pipes that we took off of the old heater. After cleaning the threads, we removed the cap on the gas valve and put a layer of gas-rated pipe dope on the threads and screwed it in tightly with a pipe wrench. We did the same for the longer piece of gas pipe, and tightened it into the 90 degree gas pipe fitting outside of the heater. Then we connected the union tightly.

We opened the valves on the meter and on the regulator outside of the heater, and allowed the gas to start flowing. Now that we had plumbing, gas and electrical, we were ready to test out heater. But it wasn't ready for us! After many failed lighting attempts, and  3 lockouts - we cracked open the gas line union and found no gas coming through the line.

Myles quickly took a pair of scissors and dug up into a brass air inlet on the side of the regulator valve. Out fell a fine yellow pollenyellow powder, and lots of it! Eventually, Myles removed the fitting for a full cleaning and it was packed with enough pollen to clog up the works, and prevent the diaphragm in the regulator from opening. After cleaning the air intake, we cracked open the regulator valve and could hear and smell the gas coming through. Tightened up the gas line union again and then spray tested our gas connections with soapy water - to ensure that no gas leaks existed.

Chapter 5: Fire it Up!

Now we were ready to test fire the heater, and with fingers crossed we hit one button on the Laars Legacy flip-out control panel. Slowly the "glow plug" began to glow to a bright red color, and then ... woosh! Such a satisfying sound to hear the pool heater fire off.

We replaced the heater door, packed up our tools, put everything back in place - and we were done, in about 2 hours.

Installing a replacement pool heater can be tricky, as you see - we ran into unexpected events at every turn. I'd be tempted to say that any handy homeowner could install a replacement pool heater, or even a new one - but that wouldn't be prudent. Working with gas and electric, as well as pressurized plumbing, can be hazardous if one doesn't have the experience or tools required. 

Here's the video we shot of the Laars Legacy LRZ heater installation.


See all of our Gas Pool Heaters in our Pool Heater Department. It's a bit easier usually if you replace with the same brand and model if possible, but no problem in switching to a different brand (Hayward, Jandy, Lochinvar, Pentair, Raypak), although you may have to modify the plumbing height for gas and water. 


- Rob