Hayward Pool Heater tips, tricks, and lessons learned

[Smykowski]

The purpose of this thread is to help out anyone in the future, so that they may not struggle with my struggles. Let my trials and tribulations be your education.

I have a Hayward H250 millivolt heater. All of this info should apply to all H series heaters, including H150, H200, H250, H300, H350, and H400. As always fix your equipment at your own risk, and if you're in over your head, call a professional.

I moved into my current house in late 2009, so 2010 was my first swim season. Our kids were young, and we couldn't justify heating the pool because we wouldn't get the use out of it. However, I recognized that the heater that was installed was a nice one, so I wanted to maintain it. Every year for (almost) the past 15 years, I've been chasing one problem or another to keep this thing functioning. It's not a statement of Hayward quality by any means. Our swim season is only 4 months long, we don't use the heater regularly, and it becomes a really attractive home for critters during the winter, so "troubles with operation" shouldn't be surprising. That said, I finally got the heater working the way it should for the first time in 13 years, and I'm sure the heater is almost 20 years old, so not too shabby. Here's a bit of knowledge, searchable on the interwebs, so that hopefully someone else can benefit from the tinkering I've done.

First, a couple of universal observations.

1. The millivolt thermopile assembly is kind of a poor design that invites problems. I've had to replace the whole thing once. Even so, it attracts dirt/debris/bugs. If the pilot won't light, one solution is to remove the nut and the machine screw, pull the whole thing out, and see if the piezo will create a spark. If it does, remove the compression nuts (one at the gas valve, one at the thermopile) and use compressed air to clean everything out. Even the smallest blockage will completely mess up the gas flow, and inhibit lighting the pilot light.

2. This thermopile generates a small voltage. That voltage travels across a circuit, and if the circuit is complete, the heater will fire. If the heater doesn't fire, there's a really good troubleshooting guide in the manual. HOWEVER, the decision tree assumes that only one switch in the circuit is defective. If only one switch is failed, the guide works beautifully. If more than one is failed, you hit a dead end, and the end result is "call someone". I think a better way is to check continuity across each individual switch. This will make it perfectly clear if/when more than one switch is failed, and which ones need to be fixed or replaced.

3. Another option is to start with the troubleshooting guide, but instead of jumping switch to switch, methodically add one switch and connecting wire at a time to determine where the breaks in the circuit are. I used this method to clean up the contacts on one of the limit switches (more in the posts below).

Over the years I've replaced the pressure switch, the system switch, and the thermopile/pilot assembly. About a year an a half ago, I determined the thermostat was bad, but at the time decided to kick the can down the road. This year, as part of the opening process, I tackled the entire system and decided to get it working. Here's what I learned....

 

[Smykowski]

First the thermostat....

I ran through the troubleshooting guide a couple years ago and determined that the thermostat had failed. In the parts list diagram, the part number is listed as CHXTST1930. However, when I searched that part number, that was not a match for the switch I had in my system. I did a little digging, and my system has part number HAXTST1930. No idea why. The important point is, a new part was gonna run anywhere from $75-$110.

I figured, if the part is already broken, I can't break it any more. (You can't over die, you can't over dry. Any Seinfeld fans out there?). I'll try to take it apart and fix it. Here's your step by step...

1. Make sure the main gas supply is off.

2. Remove/loosen the four phillips screws holding the front panels.

3. Take off the top half.

4. The thermostat knob is friction fit. Pull it off.

5. Pull the wires off the tabs.

6. Undo the screw holding the temperature limiter. Remove it.

7. This exposes the two phillips screws holding the switch assembly to the front panel. Remove them both.

8. Remove the mounting bracket by taking off the large phillips screws.

9. The next step will completely disassemble the switch. Remove the two small phillips screws.

10. Carefully separate the layers. You'll have the stem from the thermostat knob, the piece that runs to the temperature sensor, and two layers to the rest of the switch. Keep the orientation of the center stem, the frame, and the restrictor plate unchanged for reassembly! When you get to the bottom layer, you get this...

This is a normally closed switch. As the pool water heats up, it heats up the temperature sensor in the manifold. The metal runs into the switch, which also expands. Once it expands enough, it pushes down on the plunger in the layer above. This opens the switch. In my case, the contacts on this switch corroded and weren't conducting anymore.

These are the contacts that had the corrosion interfering with continuity.

I took 320 grit sandpaper and worked it in there to shine up the contact points.

Once that's finished, everything can be reassembled in the reverse order, with a few caveats.

As you complete the "switch sandwich", the flat portion of the shaft needs to be pointed to the upper left. This sets up the thermostat knob to be resting at a minimum temperature start point.

If you were able keep the stem from moving in the frame, the reassembly is easy. If you weren't careful and the stem moved, good luck, because I struggled. The trickiest part was getting the "default start point." When you remove the two small phillips screws, you'll pull off a metal plate that guards a limit plate (highlighted in the photo below, hidden under the metal plate). With the pool water freezing cold, the switch needs to stay closed. If you reassemble the switch and hear the click, you've opened the switch. You need to unscrew the stem so that the plunger doesn't actuate. The goal is to put the stem as far down as possible without actuating the switch, with the flat side pointing to the upper left. This keeps the switch closed, and allows the dial to be turned up.

Reassembly is the reverse of disassembly.

 

[Smykowski]

Sure enough, when I put the thermostat back in, the system didn't fire up. After jumping the pressure switch, it worked, so once again my pressure switch failed.

Before starting, make sure the main gas supply is off. Turn off the pool pumps. If you have shutoff valves, isolate the water. I undid the drain holes in the heater manifold to drain the part of the system I was working on. This prevents water from spraying/leaking inside the heater.

To pull the pressure switch, hold the long brass nut (which is attached to the switch), and unscrew the "further back nut". It's just a compression fitting. Disconnect the wires, and take it to your bench. This is a photo of the assembly on my kitchen table.

Part number is HAXPSA1930. Anywhere from $50 to $70 to replace. Since I had luck with the thermostat (and a few other instances of "clean up the switch" in other DIY projects), it's time to break this one open.
First, I tried drilling out the "rivet". I had better luck with a dremel, carefully grinding down the button so I could push out the pin. Once the pin was gone, the switch rotated 90 degrees clockwise, and came off the plastic pivot point.
This switch is normally open. When the pump is running, system pressure drives the plunger out of the assembly, presses the button, and closes the contact and completes the circuit.
To open it, I slid a small flathead screwdriver in the seams and gently broke the binding points, circled in green:

That revealed the inside.

It's hard to see in the picture, but after I took the entire assembly out, it became clear that there was corrosion on the contact points. I took fine grain sand paper and cleaned up the contact points, and attempted to put it back together. This is where the story goes sideways.

It was very hard to tell the orientation, and the spring was really small. Sure enough, as I was messing with it, the spring jumped out of my pliers, and flew onto the floor. I spent 5 minutes looking for it before I gave up.

The good news is, the microswitch is about 4 bucks, and is used in a whole bunch of applications. Honda Odysseys have them in a really expensive sliding door switch assembly. Microwaves use them as door open/close sensors. Went to Amazon and grabbed a pair for $8.

Put it all back together, works great.

Don't forget to turn the water and pumps back on.

A couple of caveats here:

1. I knew I only needed one normally open switch. The best deal was to buy a pair of switches, one NO, one NC. When they arrived, the little diagram stamped on the body said they were both NO. When I tested with a multimeter, one was NO and one was NC. Make sure to verify proper operation by testing it before installing it.

2. The blades on the new switch were smaller than the blades on the old switch. I don't run my heater very much, and when I do, it's pretty much supervised, so I made it work. If the heater is going to be used the way its supposed to, I would have either bought a switch with the correct size blades, or I would have put the correct size female connector on the end of the existing wiring.

3. The pressure switch comes pre-adjusted. There's a procedure in the manual for adjusting it, but I didn't do that. In the photo above, I accidentally broke the wax somewhere in my disassembly. When I reinstalled it, I put it right back to where it was.

 

[Smykowski]

One final issue I had during my ordeal happened during my original troubleshooting process. I started by jumping the two TH terminals on the gas valve to verify that the valve itself worked. Then I systematically added one section of the system at a time. The idea is that the first time the heater doesn't fire, that means the previous "section" of the circuit that I tried was the failure point.

I was having an issue right after the terminal block. On the circuit diagram, there are two "limit switches" in between the terminal block and the pressure switch. When I checked the continuity of just that section, I was getting an open circuit. One of the wires disappears towards the manifold, and the other wire comes back from it.

These switches are screwed into the manifold, and they're visible outside the panel on the back side of the heater. There are a couple of machine screws that hold the two panels in place. Removing these panels gives better access to the switch terminals and the wiring.

Once I took it all apart, I tested the continuity of each wire, and it tested fine. Then I tested continuity of both switches. Both tested fine. However, upon visual inspection (you guessed it), the blades looked like they had a little corrosion on them. I took some sandpaper and shined up all 4 blades, reinstalled the wiring, and everything worked.

In the following photo, you can see the top switch with the boot protecting the wiring circled in red. I cleaned up all four blades, but you can see the blades exposed on the bottom switch circled in green.

 

[Smykowski]

I hope this helps someone in the future.

If anyone else has issues and needs better/specific pictures, I'm happy to provide more.