Shower getting cold for one minute in the morning

[JEC54]

I installed a new rinnai v94i indoor unit 3 weeks ago. I’ve been getting cold water for about a minute in the morning . I installed a grundfos pump at the heater and the bypass valve in the master bath sink and I’m still getting cold water for a minute in the shower. The house is three stories with the heater in the basement and master bath top floor . Also I noticed when the pump comes on the heater will not run . The pump has a timer too

 

[Fitter30]

Heater needs .4 gpm to come on. Page 34 to view flow. Grundfos pump kit numbers?

https://www.google.com/url?q=https://media.rinnai.us/salsify_asset/s-43d60415-4de7-4ad8-aa59-1b39248bfe09/100000258-Value%2520Series%2520Installation%2520and%2520Operation%2520Manual.pdf&sa=U&ved=2ahUKEwje4Z735fn-AhXjADQIHXDbA04QFnoECAkQAg&usg=AOvVaw0CRLf2A_Lmxjbj083KOnla

 

[Sponsor]

 

[JEC54]

UP15-10SU7P TLC 3/4 in. NPT 115-Volt Comfort Hot Water Recirculation Pump​

My water pressure is 50psi right now so do I need to turn it up more ?

 

[Jeff H Young]

pressure is no issue, you need a minimum gpm of flow as fitter said , the model numbers are for you to research min gpm for heater to kick on. then I thinkyou need to find out how much the pump will flow on the pump specs

 

[JEC54]

pressure is no issue, you need a minimum gpm of flow as fitter said , the model numbers are for you to research min gpm for heater to kick on. then I thinkyou need to find out how much the pump will flow on the pump specs

Ok thanks and I will check that out and get back with y’all

 

[Bannerman]

You said the 'bypass' valve is located under the master bath sink. What is the piping distance between the bypass valve and the shower?

A single shower head typically has a maximum flow rate of 2.5 GPM, but many have a lower flow rate. If you are immediately setting your shower temp control to where you usually find the temperature comfortable, depending on your usual desired water temperature, the hot water flow rate maybe significantly lower than 1 GPM.

Depending on the distance between the bypass valve and the shower, at less than 1 GPM, considerable time may be needed to clear the cold water from that section of hot water line.

Since most bypass valves stop hot water recirculation flow once the valves inlet water temperature is ~100°F, additional time will be needed for the hot water arriving to the shower to rise to the WH's maximum delivery temperature (usually 120°F max).

Suggest when preparing to shower, turn on the shower control fully to 100% hot until hot water exits the shower head, then reduce the flow rate and temperature as desired before entering the shower.

 

[JEC54]

You said the 'bypass' valve is located under the master bath sink. What is the piping distance between the bypass valve and the shower?

A single shower head typically has a maximum flow rate of 2.5 GPM, but many have a lower flow rate. If you are immediately setting your shower temp control to where you usually find the temperature comfortable, depending on your usual desired water temperature, the hot water flow rate maybe significantly lower than 1 GPM.

Depending on the distance between the bypass valve and the shower, at less than 1 GPM, considerable time may be needed to clear the cold water from that section of hot water line.

Since most bypass valves stop hot water recirculation flow once the valves inlet water temperature is ~100°F, additional time will be needed for the hot water arriving to the shower to rise to the WH's maximum delivery temperature (usually 120°F max).

Suggest when preparing to shower, turn on the shower control fully to 100% hot until hot water exits the shower head, then reduce the flow rate and temperature as desired before entering the shower.

The bypass valve under the sink is directly across the shower so maybe 8-9 feet ish.

 

[JEC54]

Heater needs .4 gpm to come on. Page 34 to view flow. Grundfos pump kit numbers?

https://www.google.com/url?q=https://media.rinnai.us/salsify_asset/s-43d60415-4de7-4ad8-aa59-1b39248bfe09/100000258-Value%2520Series%2520Installation%2520and%2520Operation%2520Manual.pdf&sa=U&ved=2ahUKEwje4Z735fn-AhXjADQIHXDbA04QFnoECAkQAg&usg=AOvVaw0CRLf2A_Lmxjbj083KOnla

The pump is 6.3 gpm

 

[Jeff H Young]

Another issue with your system is its not a real circulating system they are never as good as a hot water recirculting system as it dosent get the water hot to the sink just a little warm

 

[Fitter30]

The pump is 6.3 gpm

Post 2 gave u information to see how much the water is flowing through heater. It has to be at or above .4 gpm . Then it takes a minute or so to fire heater. Pump gpm is only one part to size a pump. Pipe size, rise and length including fittings are required for accurate sizing. Every pump is different and has a pump curve for sizing that's why the all the info is needed.

 

[Jeff H Young]

could be that "cold water sandwhich" that comes with a tankless heater