Lochinvar Noble Fire Tube Combi- hot water only works when heat is on

melkru

I just bought and moved into a new house with this Combi unit. When the heat isn't on, the water gets lukewarm for about 30 sec, then back to cold, then back to lukewarm. If the heat is on, the hot water works fine.

The earliest I can find a servicer is next Friday.

Anyone have any suggestions to try?

pedmec

Is there a mixing valve on the domestic hot water leaving the boiler?

hot_rod

A flow switch triggers a valve inside, there may be a strainer that is reducing the flow that needs to be serviced. The manual, available online will have a few basic things you can check and try.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Lochinvar-NKC199N-User-Guide.pdf

How old is the unit?

PeteA

what do you mean when you say “it only works when the heat is on”? Do you mean you’re only getting hot water when the house is cold and the thermostat is calling for heat? Or when the switch or setting on the thermostat is “off”? Can you take a picture or 3 to show your heating system and nearby piping?

GroundUp

The Noble uses a priority system so the hot water will never run at the same time as the space heating. The space heating shuts off and switches to DHW whenever DHW flow is detected. It sounds like maybe your flow switch and/or diverter valve may be faulty or unplugged. If you pop the front cover off, there will be a brass valve assembly right in the bottom of the cabinet. Check all the wires and plugs on that to verify they are properly connected before hiring somebody

melkru

The unit is about 7 years old.

The hot water will only work when there is a demand for heat. So in order to have hot water, I have to turn the thermostat to a temperature hotter than the current temperature in the house.

I'll take a picture when I get home from work and will check the flow switch and diverter valve.

Thanks all.

hot_rod

The whole unit could probably use a service, the boiler it self and the DHW heat exchanger and diverter valve.

The valves can get sticky and not operate properly as it toggles from heat to DHW.

GroundUp

At 7 years old, it's long overdue for a service. It originally sounded like it was new. Either way, it's the diverter and/or flow switch giving you grief.