I've been lurking here since building my pool a couple years ago. I've finally run into a problem that I haven't been able to resolve with info from the TFP archives.
I had the dreaded mouse hotel in my mastertemp 400. I got it cleaned out and mouse-proofed, but the heater has started short cycling. I'll try to lay out all of the timeline as best I can:
After cleaning out the mice, the heater seemed to run fine, but every once in a while it would stop and show the "service heater" light. I would cycle power to the heater and it would work fine for a couple weeks. I did notice a few times that the heater would randomly kick off and restart, but it was infrequent. This issue progressively got worse until the heater wouldn't light at all.
My first serious troubleshooting (beyond cycling power) I found the heater would go through an ignition sequence 5 times and if it did not light then it would turn on the "service heater" light and stop. There are no LED error codes under the control board. When it failed to light I didn't hear any click from the gas valve and no mercaptan smell, so I assumed that the gas valve was bad. The mice had peed all over it and it looked pretty bad. Well, after replacing the gas valve it is still doing the same thing.
I then decided to replace the thermal regulator, but given that I wasn't getting the HLS led I assumed it wouldn't do the trick, it didn't.
I have a 2psi gas line to a step down right at the heater. The liquid drain hole on the heater exhaust blows hot flue gas right onto the step down regulator, so I sort of suspect maybe low gas pressure. I was able to test the outlet pressure of the gas valve during operation, it was negative 0.75 inches. During the prepurge it was about negative 5 inches. I need to get a fitting before I can test the inlet pressure to the gas valve. I was able to watch the meter while it was running and it showed about 5.5 cfm, so maybe a little bit low but probably in the ballpark.
I tried to run a separate ground wire for the ground wires near the FENWAL, but this didn't seem to make any difference. I'm also not getting any error codes on the FENWAL.
I tried running at higher pump speed (3450 vs 3100), no noticeable difference. I don't think it is a flow related issue.
I have noticed a few times where the heater seems to lose flame but immediately reignites, this seems pretty strange.
I worry that maybe there is a coil leak, but I couldn't find any drain on the combustion chamber side, I'm not sure what the best way to check this.
I wonder about the thermistors, but not really sure how to test other than simply replace them.
Other than checking the static/dynamic inlet gas pressure, I'm not really sure where to go next. Any advice would be greatly appreciated.
I had the dreaded mouse hotel in my mastertemp 400. I got it cleaned out and mouse-proofed, but the heater has started short cycling. I'll try to lay out all of the timeline as best I can:
After cleaning out the mice, the heater seemed to run fine, but every once in a while it would stop and show the "service heater" light. I would cycle power to the heater and it would work fine for a couple weeks. I did notice a few times that the heater would randomly kick off and restart, but it was infrequent. This issue progressively got worse until the heater wouldn't light at all.
My first serious troubleshooting (beyond cycling power) I found the heater would go through an ignition sequence 5 times and if it did not light then it would turn on the "service heater" light and stop. There are no LED error codes under the control board. When it failed to light I didn't hear any click from the gas valve and no mercaptan smell, so I assumed that the gas valve was bad. The mice had peed all over it and it looked pretty bad. Well, after replacing the gas valve it is still doing the same thing.
I then decided to replace the thermal regulator, but given that I wasn't getting the HLS led I assumed it wouldn't do the trick, it didn't.
I have a 2psi gas line to a step down right at the heater. The liquid drain hole on the heater exhaust blows hot flue gas right onto the step down regulator, so I sort of suspect maybe low gas pressure. I was able to test the outlet pressure of the gas valve during operation, it was negative 0.75 inches. During the prepurge it was about negative 5 inches. I need to get a fitting before I can test the inlet pressure to the gas valve. I was able to watch the meter while it was running and it showed about 5.5 cfm, so maybe a little bit low but probably in the ballpark.
I tried to run a separate ground wire for the ground wires near the FENWAL, but this didn't seem to make any difference. I'm also not getting any error codes on the FENWAL.
I tried running at higher pump speed (3450 vs 3100), no noticeable difference. I don't think it is a flow related issue.
I have noticed a few times where the heater seems to lose flame but immediately reignites, this seems pretty strange.
I worry that maybe there is a coil leak, but I couldn't find any drain on the combustion chamber side, I'm not sure what the best way to check this.
I wonder about the thermistors, but not really sure how to test other than simply replace them.
Other than checking the static/dynamic inlet gas pressure, I'm not really sure where to go next. Any advice would be greatly appreciated.