Hayward H-200 Millivolt Running Erratically

Floater22

Member
May 2, 2020
15
WNY
I was having trouble getting my heater going when I opened the pool for the season a few weeks ago. It was my first time opening the pool. A friend was able to help, so I’m confident I was following the right steps. I’ve owned the pool less than a year and the heater worked without issue for the last 6 weeks of last season that the pool was open.

Eventually got the pilot going, and it would fire, but it was having “big” startups and shutting off after <1 minute of run time. I thought maybe it was the pressure switch, or some other safety sensor shutting it down in error. Pump has good pressure, everything is clean, etc. I troubleshooted it with a multimeter and determined the pilot generator was good, and all sensors had continuity. Also checked all connections, and noticed one connection for the sensor below the burner was loose. Tightened it, and got the heater to run longer than the initial 30 second startup from before, but it was still starting abruptly. So, yesterday I decided to clean out the orifices. Much easier than I anticipated and two of them were clogged pretty badly with spider’s nests. After cleaning those, it started MUCH smoother. Had it running for an hour or two yesterday without issue and even turned it off and on again a few times. Water wasn’t hot out of the return, but from 55 degrees, it was definitely warming it. I’m not expecting hot water out of a 200k unit on a 55 degree, 19k gallon pool.

This morning I turned it on and no dice. Took the cover off, restarted the pilot, and it ran fine again. Ran it for another few hours today without issue to hopefully “shake the cobwebs off”.

So, I’m curious if any of this is normal beginning of the season type stuff, something obvious that can be corrected or if this (who knows how old) heater is on its last legs. I don’t have a spa, or heat it constantly, so it isn’t the end of the world if it’s a little finicky and I can squeeze a few years out of it. On the other hand, these Millivolt heaters seem like simple machines, so if its a $30 sensor, I’d love to extend the life.
 

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swamprat69

Well-known member
Mar 30, 2019
250
Las Vegas, NV
Without knowing how often your heater has been cleaned/serviced, dirt may be your biggest problem and lead to other problems. Burners should be cleaned inside and out on a regular basis. On a millivolt system, you may have a weak or restricted pilot flame due to accumulations in the pilot orifice ( between the pilot tubing and the pilot assembly) or a partial blockage at the pilot assembly outlets where the flame comes out of the pilot assembly.
 

Floater22

Member
May 2, 2020
15
WNY
I think the pilot looks faint, but my friend who helped me is a pool owner and he seemed confident it was sufficient. Also, the generator was reading 430-500 on the multimeter which is “good” from what I’ve read. Not sure if that completely rules out the pilot being weak.

I know the previous owner and they said they didn’t have frequent issues with it, but also weren’t scrubbing the thing clean every year or paying a pool company to do so either. I did clean any leaves and debris out with my shop vac and would say it looked fine inside for its age. It wasn’t spotless, but no crazy corrosion, nests, or anything.

Anyway, is cleaning the pilot orifice/ tubing a DIY endeavor? The pilot seems buried in the unit, whereas the main burner orifices are right up front.
 

swamprat69

Well-known member
Mar 30, 2019
250
Las Vegas, NV
This should be the manual for your heater: https://hayward-pool-assets.com/ass.../manuals/h-series-millivolt-owners-manual.pdf. Page 15 / Figure 30 shows the wiring diagram for a millivolt system. How are you taking your millivolt readings? If you are taking your readings at the 2 screws on the gas valve that the thermopile leads are connected to with just the pilot on you can be introducing some variance in to your readings because of corrosion at the connections. Your reading should be pretty steady. Clean both the thermopile lead clips and the connecting plate and under the screw head at the gas valve (small wire brush or small diamond file available at harbor frieght or amazon). This should give you a true and more stable reading of the actual output with no load. You also need to take a load reading while the system is is either running or trying to run. Your whole system runs using less than 1 volt. If you look at the figure 30 wiring diagram you will see that this small voltage runs through multiple safeties, a thermostat and an on/off switch. Any significant voltage drop through through these due to dirt or corrosion at the connections to these or in the internal switch can be enough to cause the gas valve to drop out. Most thermopile gas valves will not have enough voltage to operate the valve if it drops below 110-120 MV under load. Individual safeties and switches can be checked for voltage drop by taking a reading across each individual safety or switch. According to the wiring diagram your load readings should be taken between TH and PP on the honeywell valve and TH and TP on the robertshaw valve. Let me know if you identify any weaknesses with this information and we can go on to any problems with the pilot if needed.
 

Floater22

Member
May 2, 2020
15
WNY
I did reference the manual when I did my initial checks, but was also following a YouTube tutorial. I will plan to go through the whole system again checking connections and voltage readings. I’ll admit I’m not experienced with a multimeter, so the circuit aspect of this thing is not my strong suit. Now that it’s not shutting itself down I should be able to get better readings under load.

Someone else suggested checking the flow of the bypass valve by removing the drain plug. I plan to do that as well.

Really appreciate the help. Of course this could be solved with a phone call and a few hundred $$, but I’m stubborn about trying to fix things myself. Appreciate your patience in leading the “blind”.
 

Floater22

Member
May 2, 2020
15
WNY
Didn’t want to leave this open ended. Checked everything again and didn’t find any issues. Ran it a few times in the last week and no issues. Glad I got the kinks worked out before swimming weather.