Instant Hot Water Heater Blew Up, Billowing Smoke

[Pib]

Well, the Fagor repairman showed up...my heater is now working again. Turns out he only had to reset the two thermal fuses in the unit. These two thermal devices are mounted on the two heating elements. I had noticed these devices when looking at the inside of the heater, but they didn't look like they were resetable in any way, but they were. The repairman pressed 2 tabs on each thermal fuse...these tabs were sticking up out of the middle of the fuses and just looked like unused electrical connections. Six tabs exist on each thermal fuse, with wires soldered to four of the tabs.. as mentioned, the 2 reset tabs look just like two unused electrical connectors/tabs. Anyway, he pressed the two tabs on each thermal fuse (the tabs then returned to the exact same position before pressing. He then turned on the hot water faucet and the heater is working again. I had him show me again exactly how he reset the fuses and he explained the two tabs that just looked like electrical connectors are thermal fuse reset tabs...press each tab once and it resets the device. The manual had implied that he heater may come with reset-able thermal fuses, but didn't go into any further detail/show any pictures. Although the heater had a warranty for 3 years, that was on parts only...the warranty on service labor was only 1 year. It cost me 500 baht for his 10 minutes visit...he came to my western Bangkok home from central Bangkok. 2 day service.

Now what caused the heater fuses to blow? Well, although I didn't mention it in my earlier posts I think it was an air bubble in the water pipes. As I was finishing my shower and turning off the hot water faucet I noticed the water spit-and-sputtered some air for about a second. That's when the heater stopped working with a noise and light flash...the noise was probably the thermal fuse tripping and the flashing was caused by the Power-On LED. Regarding the spit-and-sputter, it was like when the water has been off or you been working on the water pipes, the water comes back on, you turn your faucets on, and they blow a mixture of air & water for a few seconds until all the air gets out of the pipes. I figure doing that second when mainly air was flowing through the heater that the elements got much hotter than normal, and the thermal fuses did their job and tripped. We all know you don't run a water heater without water in it as it will cause the heating elements to overheat very quickly, and even burn out. Now, I wasn't knowing running the heater without water in the lines, but somehow, someway, there was about a one second air bubble than came through the pipe that caused the heater to "overheat" and its thermal fuses did their job. My 850 liter water storage tank is full and the pump working fine; it was only that one second air bubble that somehow got into the pipes. Would be nice if the thermal fuses would reset automatically after X-minutes like some thermal devices, but instead they must be manually reset by removing the heater's cover "and knowing the secret on how to reset them"....I now know that secret for the next time if it occurs again.

[Pib]

It cost me 500 baht for his 10 minutes visit...he came to my western Bangkok home from central Bangkok. 2 day service.

Correction: I thought today was Wednesday...too much Chang beer....I meant 1 day service...called yesterday/Monday morning, the repairman arrived today/Tuesday morning. Gives an indication of how responsive Fagor At Home Repair Service is.

[Pib]

Didn't mention it in my Post 31 above, but after the repairman reset the heater's internal fuses I saw him also adjust a screw in the heater while looking at the shower head flow output, heater-on LED light, and turning the hot water faucet control back and forth slightly to make the LED go on and off. I figure he may be adjusting the minimum flow rate required before the heating elements will switch on. But I just hate it when someone does an adjustment relating to pressure, flow, etc., without using the a proper measuring device/method like such as a pressure gauge, flow rate gauge, actual time-volume measurement, etc. Summary: he make a flow guesstimate by visual means.

Anyway, after he left I looked at the manual again and it didn't say anything about the screw he was adjusting, but there was one diagram that showed the screw adjustment as being part of the differential pressure device. That was enough to confirm to me he was "looking" for a minimum flow rate before the heater would kick in. A minimum flow is needed to ensure enough water is flowing through the water coils the heating elements/coils are sandwiched against, otherwise the heating elements/coils could burn themselves up, trip circuit breakers, etc. Kinda like if your car radiator would lose part/all of its water your car engine could overheat/burn-up. I found a specifications in the heater's manual saying it would produce a "minimum" 3 liters flow per minute with the water heated to 37C...so I decided I would use this flow rate as the required point the heating elements should switch on.

To check the flow I got a 1.25 liter plastic Pepsi bottle, used my measuring cup to mark off 1.0 liter on the bottle, took the shower head off so I could put the hose end into the bottle, turned the hot water faucet on just until the heater kicked on, placed the hose in the bottle top, made a 20 second water flow measurement into the bottle, multiplied times 3 to make it equivalent to flow reading over a one minute period. Repeated this process several times while making small adjustments to the heater's differential pressure device until I got a 3 liters per minute flow when the heater just kicks on. Before doing the adjustments, I had a 2.5 liter per minute flow when the heater kicked-in, which means the heater may have been kicking on a little before its specifications minimum flow rate setting, which also means possibly not enough water would be flowing through the heater at a low hot water faucet setting which could cause the heater to fail early.

I feel more comfortable now that the heater flow/heater-on setting is correct since I used a measurable flow rate method versus the repairman who just "visualized" the flow rate. Maybe he was just using the approach, "That's Good Enough for Government Work."