Why does my shower get cold ??

I have a hot water circulator that has to be manually activated. Before showering, I use the circulator and the shower starts off hot. As the shower is running, the water gets colder and colder. If I activate the circulator when the shower gets cold, the shower gets hot again (actually too hot). I have my water heater set at 125 and the shower itself is close to the water heater. It just seems that the hot water does not flow fast enough during a normal shower to maintain the temperature & it requires that the circulator be activated during the shower so that the temperature does not get too cold. Are there any other adjustments that can be made so that I do not have to always have to activate the hot water circulator during my shower?

Thanks for any ideas.

It sounds like your hot water circulating pump is drawing hot water away from the shower somehow. I do not have a solution for you, but I expect that that may be the source of your problems.

Check the Tempering Valve If You Have One

I have a tankless coil hot water heater in my hydronic boiler and was getting cold showers in the winter when the water supply got down to about 36F. The problem was that the tempering valve got stuck and was keeping the cold water inlet to the valve open.

An easy immediate fix was to take the control stem out of the tempering valve. Not safe if your water heater is too hot and you have kids who might scald themselves.

It is possible the CNM is having a problem with his hot water production, but the fact that the water starts hot, quickly turns cold then gets hot again once he starts the recirculating pump seems to suggest that hot water is available, but just not getting to his shower. That got me thinking that it might be related to the pump rather than the hot water heater.

Sounds to me that the check valve in the recirculator is broken (you do have one, don't you?). This would allow cold to cross over to the hot side, giving you cold on both sides unless the pump is on to force hot into that part. My unprofessional opinion.