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I experienced a diverter problem. The diverter works fine when I the hot water flow out the tub spout, but switch it to the shower and hot water will become cold after couple minutes. I switch to the tub spout again, it will become hot after a while. I tried to change the cartridge, and adjust the cold water pressure. It is the same situation. Could anyone help me? Thanks!

  • Do you have a tankless water heater? If so, it may be that the flow through your shower (if is is a lower flow head like 1.5 gpm) is so low that the water heater is shutting off. Tankless water heaters require a certain minimum flow to operate. If the flow is below that minimum the heater stops heating the water flowing through it. If you tankless water heater that is not staying on, see if running hot water from another tap (like the lavatory hot faucet) simultaneously with the shower will keep the water out the shower hot. The minimum flow for heating may be adjustable. – Jim Stewart Mar 27 '18 at 18:51
  • Another solution to the problem of the tankless heater shuting off with a low flow shower head is to lower the output temp of the water heater. To get the same shower temperature you will increase the flow from the hot water heater so that the heater stays on. Try 115 F or even 110 F. But if you want 120 F say for the dishwasher to work or for multiple showers simultaneously, use a higher flow shower head. – Jim Stewart Mar 27 '18 at 19:00
  • @JimStewart Many newer tankless water heaters have pretty low activation thresholds (~0.4 GPM) and even lower continuous thresholds (~0.2 GPM), so I'd be surprised if that was the cause, assuming a relatively modern tankless – Hari Ganti Mar 27 '18 at 22:59
  • The other possibility is that the mixing valve is a pressure balancing type and the lower flow of a shower head is causing it to fail. It would be nice if the OP would give more information. – Jim Stewart Mar 28 '18 at 2:00
  • Thanks Jim and Hari! I am living at condo, do not have any tank at my department, I have two bathroom, only one has this problem, the cartridge is new one, try to adjust the pressure of hot water and cold water pipe , can not solve the problem. Thanks again! – bill.q Mar 29 '18 at 0:32

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