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I just completed my third tankless install in the last 2 years. Obviously I don't have a wealth of experience with these although I look forward to selling the snot out of them in the future.
I finished last night around 9:00 p.m. (didn't start until 12:30 p.m.). I get a call this morning from the ho stating that water is pouring from the relief valve. Pressure was fine pre install but I had to relocate the existing prv in the crawl space and now I'm wondering if it should have just been replaced it whether it was bad or not? I moved it back upstream about 6' on a galvanized system in order to access 3/4" piping. Yes I'm nervous about this install on galvanized but was able to inspect the interior surfaces of the galvanized and it was remarkably clean. Of course there was evidence of light surface rust but no full blown decay of the pipe. There remained about 10' - 15' of 3/4" galvanized piping upstream of my supply connection to the wh which was run in pex and of course the service from the meter to the house is most likely galvanized. I'm thinking that the relocation of the old exisiting prv may have shook loose some scale or something and has rendered the prv ineffective.
Could another possibility could be thermal expansion? I have not experienced this with either of the other two units I have installed (Rinnai, Takagi, and this was my first Noritz). I read something on Noritz's website about thermal expansion the other day before I installed it but dismissed it not understanding how you could have thermal expansion with a tankless. Today as I think about it more I think I can conceive of a possible scenario and want to see what anybody thinks.
Ok, here it is. Hot water is being used in the house and as soon as demand ceases, the burner shuts off but their is residual heat built up in the heat exchanger which continues to heat the water for a short time, which creates thermal expansion past 150 psi, which opens the relief valve, which could (if flow is large enough) constitute a hot water demand since it is downstream of the heater, which will cause the burner to turn on, which creates an endless cycle.
Am I wrong? Has anybody witnessed this? It seems silly to me to install an expansion tank for a tankless water heater, but now suddenly maybe not quite so silly.
I will be returning in the morning to check everything out but am hoping to get some input from anybody that has a lot more experience with these than I do.
I finished last night around 9:00 p.m. (didn't start until 12:30 p.m.). I get a call this morning from the ho stating that water is pouring from the relief valve. Pressure was fine pre install but I had to relocate the existing prv in the crawl space and now I'm wondering if it should have just been replaced it whether it was bad or not? I moved it back upstream about 6' on a galvanized system in order to access 3/4" piping. Yes I'm nervous about this install on galvanized but was able to inspect the interior surfaces of the galvanized and it was remarkably clean. Of course there was evidence of light surface rust but no full blown decay of the pipe. There remained about 10' - 15' of 3/4" galvanized piping upstream of my supply connection to the wh which was run in pex and of course the service from the meter to the house is most likely galvanized. I'm thinking that the relocation of the old exisiting prv may have shook loose some scale or something and has rendered the prv ineffective.
Could another possibility could be thermal expansion? I have not experienced this with either of the other two units I have installed (Rinnai, Takagi, and this was my first Noritz). I read something on Noritz's website about thermal expansion the other day before I installed it but dismissed it not understanding how you could have thermal expansion with a tankless. Today as I think about it more I think I can conceive of a possible scenario and want to see what anybody thinks.
Ok, here it is. Hot water is being used in the house and as soon as demand ceases, the burner shuts off but their is residual heat built up in the heat exchanger which continues to heat the water for a short time, which creates thermal expansion past 150 psi, which opens the relief valve, which could (if flow is large enough) constitute a hot water demand since it is downstream of the heater, which will cause the burner to turn on, which creates an endless cycle.
Am I wrong? Has anybody witnessed this? It seems silly to me to install an expansion tank for a tankless water heater, but now suddenly maybe not quite so silly.
I will be returning in the morning to check everything out but am hoping to get some input from anybody that has a lot more experience with these than I do.