请问一个Tankless Water Heater 时时断热水的问题

有个出租房，1922年的，有个洗澡，热水汀暖气二用的热水器坏了，十年新，洗澡时用几分钟就断热水。下面房客写来的，请问会是什么问题？

"The shower goes cold, not gradually but suddenly for about 3 minutes in the middle of the shower about 3 times a week.  I take on average 10 minute showers, I would estimate that it happens a couple of minutes into the shower.  There does not seem to be any correlation to anything - something else running, previous use, amount of time of use before- nothing.  There is no warning, it happens and then gradually reheats."

所有跟帖： 

• what is the temperature setting? if -calvinwch- ♂ (79 bytes) () 08/30/2017 postreply 06:18:43

• 这个没查，谢谢。但是在北加州，又是厦天，天应该不冷 -空麻袋- ♂ (0 bytes) () 08/30/2017 postreply 07:54:08

• 北加州,三藩巿現在是54度 -calvinwch- ♂ (301 bytes) () 08/30/2017 postreply 08:15:32

• 除去人为改动设定，可检查 -上海大男人- ♂ (256 bytes) () 08/30/2017 postreply 06:27:37

• 水位空置？？ -calvinwch- ♂ (78 bytes) () 08/30/2017 postreply 07:51:03

• 谢谢。这个换一个大概多少钱？ -空麻袋- ♂ (0 bytes) () 08/30/2017 postreply 07:55:10

• 整个换掉 -空麻袋- ♂ (0 bytes) () 08/30/2017 postreply 07:55:34