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# Slant/Fin hot water shower issue

Member Posts: 5
edited April 2021
I have a Slant/Fin sealed combustion boiler model no. LX-85A with a storage tank.

After about 8-9 minutes, the hot water basically turns cold/lukewarm. The domestic hot water supply setting is set at 160F.

What is my issue here?

• Member Posts: 5,365
edited April 2021
This is the beginning of an algebra problem where you don't have all the variables We already know that 1 BTU will raise the temperature of 1 pound of water 1 degree farenheight. We also know that there is a maximum of 85,000 BTUs available in any given hour. We can assume the boiler will use those BTUs to transfer to the water at an efficiency rate of about 94%. We also know that water weighs about 8 pounds 6 ounces. With this information, we can calculate what amount of water will be heated from any given temperature to any other given temperature in any given time frame. Simply put you can make about 2.7 gallons of water change from 58°F to 118°F every minute.

The other variables are the amount of water stored in the tank, the lag time from the water tank temperature sensor indicating the need for the burner to operate, if the burner is operating at full capacity and if there is any off cycling during the need to make hot water.

If you are drawing more than 2.7 gallons per minute, and the burner is not activated on a timely basis and the burner does not operate at full output, then you will deplete the hot water in a short time frame.

Now that the math problem has started, let's fill in the blanks or variables.
1. What size pipe connects the boiler water to the indirect tank heat exchanger?
2. What is the boiler water temperature high limit set for?
3. What is the HOT water tank thermostat connected to?
a. Zone valve,
b. Zone Valve Control panel,
c. Circulator pump,
d. Circulator zone panel,
e. DHW terminals on the Slantfin Boiler Controller,
f. Other.

4. What size is the DWH tank? (or model number)
5. Finally, We like pictures. lots of pictures. From far enough away to see the pipes and how the boiler is connected to the water tank and the rest of the system. From several different angles.

If you can provide us with the info, and we can go further with the solution.

Yours Truly,
Mr.ED

Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
• Member Posts: 5
Hi Mr. ED, for some reason it is not allowing me to post the pictures to this website. Do you have an email that I can you to the pictures too?
• Member Posts: 2

• Member Posts: 2

• Member Posts: 105
The aquastat on the storage tank is set at 160F you say?  If so, although the storage tank is on the small side (30 gallons?) it should have decent capacity for more than 9 minutes of consumption.  A mixing valve added to the storage tank should be there, a 160F is very hot and the mixing valve will make the small tank perform like a much bigger one.
• Member Posts: 5
Ctoilman said:
The aquastat on the storage tank is set at 160F you say?  If so, although the storage tank is on the small side (30 gallons?) it should have decent capacity for more than 9 minutes of consumption.  A mixing valve added to the storage tank should be there, a 160F is very hot and the mixing valve will make the small tank perform like a much bigger one.
I believe there is a mixing valve in place. Would this suggest that it is faulty?

And thanks for the response!
• Member Posts: 105
I didn't see a mixing valve in the pics you included, but if there is one I'd strongly suspect that is the problem, as they don't last but typically easily fixed/rebuilt.  The Honeywell model has been a great performer with tough water quality, AM-100 model I believe.

• Member Posts: 5
Thank you for the input, I will look into it
• Member Posts: 7,370
Is that a rebranded 20 gallon superstore? The transfer rate of the coil may also be a limiting factor.
• Member Posts: 5
mattmia2 said:
Is that a rebranded 20 gallon superstore? The transfer rate of the coil may also be a limiting factor.
I am not sure if it is but i’m told it holds approximately 40 gallons. I’ve asked the landlord to send someone to diagnose the issue, hoping for a timely evaluation and intervention.