Flow switch reccomendation for hot water recirculation system

[1audio]

My house was built in the 1950's with a dedicated hot recirculation system. It is quite unusual in the bay area but the "architect" specialized in large commercial systems. It all works. I had to replace the water heater and I had a tempering valve installed at the same time. Overall its all working except the water flow for a shower is not quite enough for the tempering valve when the recirculation pump stops. There is a temperature switch on the return which cycles during a shower.
What I want is an inline flow switch that I can connect n parallel with the temperature switch to keep the pump runnung when water flow is detected. The options I have found do not seem suitable- either the wrong type of pipe thread and/or a hall evffect sensor which would need electronics or switches with paddles that are unclear in their application. Are there any reccomendations for a flow switch (not sensor) 120V 1/2 gpm 3/4" NPT fittings?

 

[Breplum]

What is the temperature switch (pics) name and model?
pix of the whole setup would be ideal. or drawing of the layout.

 

[Sponsor]

 

[1audio]

Here are pictures of the installation. The house is a rancher and the showers are 50' from the water heater so the loop is 100'. Its all copper.Even the sprinkers outside were plumbed in copper.
The temperature switch is a Mercoid. Its part of the original install but a new replacement. https://dwyer-inst.com/en/series-da...BrQ3vVz7zQFrhe_KWZi0F6HfOvRcDel6FJPK6YA_sTytq I did NOT pay that price. It seems to work fine.
The tempering valve is a Honewell AMX3. The return line goes to the tempering valve per the honeywell instructions.
The water heater is running around 135F. The tempering valve is set to 120F when the flow is high. However a modern shower head is 2 GPM. and the 120F is mixed to get it down to 100F or so. The switch is at the return line and when the pump stops the water there stops and it slowly cools from convention. Then the tempering valve flow is too low and the output gets hot.
I have a 4 input thermocouple gauge on the wall (This stuff is so cheap today) to monitor input and output temperatures.
My plan is to parallel the flow switch with the temperature switch so the pump runs continuously when there is hot water draw. The switches on Amazon all have some aspect thats not right. Either a BSP thread (not a taper thread) or they need to connect to some electronics. I think adding a microprocessor to a switch is stupid and unnecessary.
I was toying with using a PID controller on the pump but it might impact the pumps life to have lots of short cycles. And I would need to run a thermocouple to the other end of the house.
I hope this is not too much info. . .

 

[Fitter30]

Exactly what do u want to do? They make adaptor fittings bps to mpt. Your problem return line goes into the tank drain. Cold goes into mix valve which is a constant temp. F switch doesn't have n.o. contacts want n.c. or the opposite simple one pole double throw relay. Need a diagram? Have you done any maintenance on the mix valve shouldn't have that big of swing in temp. Buy another cartridge change it out soak old cartridge in vinegar for a few days. Then have a spare for a easy swap.

https://www.amazon.com/dp/B086W6L12F/ref=sspa_dk_detail_4?pd_rd_i=B086W6L12F&pd_rd_w=dTcbq&content-id=amzn1.sym.953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_p=953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_r=V9VNBAFHCMEVD20H3D6S&pd_rd_wg=BPSWZ&pd_rd_r=37e5dd87-54ca-4faa-bb6e-37c8d8e56649&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWwy&th=1

 

[1audio]

Exactly what do u want to do? They make adaptor fittings bps to mpt. Your problem return line goes into the tank drain. Cold goes into mix valve which is a constant temp. F switch doesn't have n.o. contacts want n.c. or the opposite simple one pole double throw relay. Need a diagram? Have you done any maintenance on the mix valve shouldn't have that big of swing in temp. Buy another cartridge change it out soak old cartridge in vinegar for a few days. Then have a spare for a easy swap.

https://www.amazon.com/dp/B086W6L12F/ref=sspa_dk_detail_4?pd_rd_i=B086W6L12F&pd_rd_w=dTcbq&content-id=amzn1.sym.953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_p=953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_r=V9VNBAFHCMEVD20H3D6S&pd_rd_wg=BPSWZ&pd_rd_r=37e5dd87-54ca-4faa-bb6e-37c8d8e56649&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWwy&th=1

Per the instructions from Honeywell the return goes to the fitting on the tempering valve. I missed the requirement to set the temperature 27 degrees higher than the tempered value. I'll try that and see what happens.

 

[Breplum]

I see your return line does NOT go into the drain. Frankly, that is where I would pipe the return line and just have hot output going to feed the hot supply. That keeps it simple. That should not affect flow to the shower, which is your stated issue.
All of us plumbing contractors have piped what I am describing (recirc system with tempering valve) without needing 'keep pump running' switches and never have issues.

 

[1audio]

it turns out the problem was buried in the directions- something that was not obvious in the manual that came with the tempering valve. It really needs the 27 degree F difference between hot in and tempered out. Turning the water heater up to 150F seems to have compleatly resolved the issue. 10F was not enough to get regulation.

 

[1audio]

I just reviewed the directions for the AMX3. There is NO mention of the required difference between the hot temp and the regulated temp. A real oversight I think.

 

[Fitter30]

https://www.amazon.com/DIGITEN-FS-C02-Brass-Switch-0-220V/dp/B07QNN3R6G/ref=pd_sim_hxwPM1_sspa_dk_detail_d_sccl_4_1/133-4569557-8983324?pd_rd_w=MiQ3Y&content-id=amzn1.sym.3a852a98-d65f-4301-9bd0-9b589b14d1ef&pf_rd_p=3a852a98-d65f-4301-9bd0-9b589b14d1ef&pf_rd_r=JSSF5C8VBYMJ59HMWEYF&pd_rd_wg=xmrs1&pd_rd_r=38e1acd8-1077-4db2-b630-f32333a536e1&pd_rd_i=B07QNN3R6G&psc=1&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM=