HTP UFT 80w - running out of hot water too quickly

[bbender716]

Hi all, apologies for my relative lack of knowledge compared the average member here.

Just moved into a new home with radiant floor heating powered by an HTP UFT 80w combined with a storage tank for hot water. I'm new to both tankless and radiant flooring but the previous owner was an HVAC and specialized in radiant flooring.

The current issue is that we run out of water relatively quickly. A 10-15 minute shower but definitely not enough for a bath. In terms of equipment we have the HTP UFT80w, and a Grundfos Comfort Recirculator (running on Auto). The settings on the HTP are dizzying but are all relatively close to the installer default, except the outside min/max settings that match the local area 99% values. I did reset the circuit these were on for an unrelated reason at some point but I don't think that changed anything.

Any ideas on what settings to check on the HPT or suggestions to increase hot water supply without sacrificing too much efficiency?

Home is a 2400 sqft ranch built in the 1960s.

Thank you so much for your help and patience!

-BB

 

[Dana]

How big is the tank, and what is the storage temperature set to?

 

[Sponsor]

 

[NY_Rob]

Shame the OP never came back... the UFT80-W can actually supply all the hot water he needs if setup correctly.

 

[Dana]

I agree. It would be useful to know what his settings are. A picture of the installation might tell us something too, but I suspect this is primarily about the settings (on either the boiler, the tank, or both.)

 

[bbender716]

I agree. It would be useful to know what his settings are. A picture of the installation might tell us something too, but I suspect this is primarily about the settings (on either the boiler, the tank, or both.)

I'm back! Sorry guys. Let me grab some settings. Most are near default but I adjusted the couple of setting specific to the water table temp of my location.

When I shower, I get around 10 minutes, then cold water, then I ran downstairs and at least confirmed the tankless was running. Read something like 163 degrees but don't know what that means. I'll post a picture of our setup... What settings are most pertainent that you want to know? (Symbols ideally since I don't know what they all mean :/ )

Thanks guys!

 

[bbender716]

Here's the tank, tankless, and hookup to the circulator. Some settings here as well...

 

[bbender716]

More settings...

 

[bbender716]

@Dana @NY_Rob thanks guys!

 

[Dana]

I'm back! Sorry guys. Let me grab some settings. Most are near default but I adjusted the couple of setting specific to the water table temp of my location.

When I shower, I get around 10 minutes, then cold water, then I ran downstairs and at least confirmed the tankless was running. Read something like 163 degrees but don't know what that means. I'll post a picture of our setup... What settings are most pertainent that you want to know? (Symbols ideally since I don't know what they all mean :/ )

Thanks guys!

What tankless is running?

The UFT-080W is a wall hung boiler, not a tankless (ergo the need for a SuperStor tank full of domestic hot water).

This boiler has separate ports for space heating and the domestic hot water heater. The water heater's heat exchanger is normally hooked up to the connections at the bottom of the boiler, the space heating normally at the top. See the diagram on p.20 of the manual.

There is a sensor in the indirect water heater wired to the system controls which determines when it needs more heat. The details will vary, so you're going to have to dig deep into the manuals. I'm not inclined to go through each line item in the UFT-080W manual to figure out how you have it set up, (but YOU should walk through it all and figure it out.) Parameter 21:dH is the tank's set point parameter (which you didn't document), 22:dd is the temperature drop below the setpoint where it begins to call for heat, which you currently have set to 10F. If the setpoint is 120F and it doesn't fire the boiler until it drops to 110F that could be an issue for showering, but if the setpoint is 140F and it starts calling for heat when it drops that 10F to 130F it isn't an issue, since a normal showering temp is ~105F. Parameter 24:st is the boiler's output temp when serving the tank, currently set to 175F, which is fine. See p. 52 of the the manual for other domestic hot water parameters.

The potable cold water feed to the indirect should be connected to a port on the bottom, the hot from a port near the top. See the plumbing diagrams on p.10 of the SuperStor manual to help figure out if yours is plumbed properly.

It's worth figuring out where to set the other parameters too. You currently have the minimum supply temp for heating at 130F, which might be giving up some condensing efficiency, but it might need to be that high to keep from short cycling during the shoulder seasons, depending on your radiation type/amount.

 

[bbender716]

What tankless is running?

The UFT-080W is a wall hung boiler, not a tankless (ergo the need for a SuperStor tank full of domestic hot water).

This boiler has separate ports for space heating and the domestic hot water heater. The water heater's heat exchanger is normally hooked up to the connections at the bottom of the boiler, the space heating normally at the top. See the diagram on p.20 of the manual.

There is a sensor in the indirect water heater wired to the system controls which determines when it needs more heat. The details will vary, so you're going to have to dig deep into the manuals. I'm not inclined to go through each line item in the UFT-080W manual to figure out how you have it set up, (but YOU should walk through it all and figure it out.) Parameter 21:dH is the tank's set point parameter (which you didn't document), 22:dd is the temperature drop below the setpoint where it begins to call for heat, which you currently have set to 10F. If the setpoint is 120F and it doesn't fire the boiler until it drops to 110F that could be an issue for showering, but if the setpoint is 140F and it starts calling for heat when it drops that 10F to 130F it isn't an issue, since a normal showering temp is ~105F. Parameter 24:st is the boiler's output temp when serving the tank, currently set to 175F, which is fine. See p. 52 of the the manual for other domestic hot water parameters.

The potable cold water feed to the indirect should be connected to a port on the bottom, the hot from a port near the top. See the plumbing diagrams on p.10 of the SuperStor manual to help figure out if yours is plumbed properly.

It's worth figuring out where to set the other parameters too. You currently have the minimum supply temp for heating at 130F, which might be giving up some condensing efficiency, but it might need to be that high to keep from short cycling during the shoulder seasons, depending on your radiation type/amount.

Looks like the dH is at 145 but the (tt) which I assume is tank temp is at 132 and yet it doesn't show as firing. Also when I look at the screen without selecting any options it says 125, but when I hold the heat button it flashes 132, and the setpoint is at 145! I am truly lost.

Also the superstor looks to have no dial/adjustment on it so I assume it's controlled through the boiler interface...

 

[Jadnashua]

The temperature sensor may not be properly seated in the well of the indirect WH...therefore, it can't sense proper temperatures. Normally, though, it would end up being hotter than settings, since it would be sitting closer to the outside, and not where it was designed to be. It's also that the sensor is not working properly, but they're pretty reliable.

I didn't look carefully, but assuming you have a tempering valve on the tank, it may not be working properly.

 

[Dana]

Tempering valves and thermostatic mixing valves are usually pretty reliable, but that is a possibility. The pictures of the near-tank and near boiler plumbing are impossible to decipher to figure out if it's even plumbed correctly. If the heat exchanger or potable water connections are in backward it could result in an apparent-capacity problem.

If the tank sensor is the wrong one or has drifted way off calibration the storage temp may be lower than programmed. If it's set to 145F you have plenty of headroom for bumping it up. As long as there is a tempering or thermostatic mixing valve at the output (required by code now), it's scalding-safe to program the storage temp to 160F, which would still leave you a decent delta-T on the boiler's max output temp, and should provide more apparent capacity if sensor calibration/drift/type is the problem. Measuring the temperatures independently could be useful for diagnosing this.

 

[Jadnashua]

FWIW, one thing that surprised me on my HTP indirect is a statement in the manual that says a maximum storage temperature of 140-degrees. I'm not sure what their reasoning for that is, but check yours to see if it's in there.