Hot water turns cold after 2 minutes

Dean_16

I have a 700 square foot rental unit with a small hydronic system and hot water coil. The is very hot for a minute, then settles back to 110 or so, then turns cold after 2 minutes. The thermostat on the boiler is set for 180 degrees and the space heats well.

Is this a common symptom for something? leaky or corroded coil? Bad thermostat?

ScottMP

Dean

Two Things come to mind.

1) The coil is older and its walls are lined with mineral deposits this slows down the heat transfer. As the water sits while not being used it has time to transfer heat but when the flow starts it can't keeo up.

2) The mixing valve ( if there is one ) is defective and needs to be replaced.

Easy to find out which it is. Feel the pipe, carefully it could be real hot, as it leaves the boiler. If its stays real hot and after the mixing valve its cool its the valve. If its turns cold, just like your faucet, its the coil.

Either way you need a contractor to repair the situation. Tenants don't like cold showers

Scott



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Mitch_6

do you have

priority control on the heating system that does not allow the heating circulator to run when the boiler is to cool.

Mitch S.

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clammy

well pump

Is your water supplied by a city or are you on well water ?If your on well water check your well tank and see if there is still a air charge on the diapharm of the tank check the pressure if the tank has no pressure as the pump turns on you get less warm water because there less of a pressure drop on the cold line it's when the pump comes on the water takes the path of least resistance and your shower or faucet goes cold if your on city water check the mixing or tempering valves as other have mentioned you can also check and see if you have a large pressure drop across the coil if so you may need to get your coil cleaned or replaced depending on age if so maybe it's time to put in a indirect hot water heater and then your boiler would not have to maintane temp for domestics hot water production and you would have more avaibable hot water good luck and peace clammy

bob young

COULD BE A CLOTHES WASHER BYPASSING

Joe Brix

Hows the aquastat

There should be a low limit set of no less the 140-160°.
Does the boiler fire to keep a min temp, not just when a zone calls. The aquastat could be faulty.

Joe Grosso

HW

You need someone who is experienced in troubleshooting and/or cleaning coils, and can check for things like washing machine by-passing, etc.
If the flow is good, it probably is not a scaled coil.

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