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Question DetailsAsked on 4/30/2018

Why do I have heat but no domestic hot water?

About a year ago we had a Purepro Advantage Oil Burner installed. Its supposed to heat both our water and radiators. When we turn the hot water on its hot for about 30 seconds then runs cold again and stays cold but our radiators are heating up just fine.

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1 Answer


There are several ways system hot water heating can be plumbed - direct from boiler or with a separate hot water retention tank, etc - sseveral possibilities.

The flow from the tank or boiler is generally at near boiling (temp needed for the hydronic heating system) so there is a thermostatically controlled mixing valve which blends that hot water with cold water to provide your domestic (commonly 120-140 degree) water. This has a safety device to prevent full-hot water from entering that system, and is supposed to be designed so if it fails it shuts off the hot water flow. My suspicion, since you have hot water for area heating and are getting an initial shot of hot water is that too much hot water is coming through so that safety shutoff so it is then choking off the hot water flow through the mixing valve, and letting only the cold water through after that point.

Depending on your plumbing, there are other possibilities but with the hydronic heating working correctly that would be my guess as the cause.

Heating and A/C (ideally the company that installed your system if you liked their work) would be the Search the List category to repair this - probably about $75-350 service call charge (around $125-175 in most of the country) should handle it. Plus the mixing valve, if replacement is needed, can be from around $150-250 range (for common brands like Sharkbite or Watts) on up to $1000 range (like for a Leonard or Siemens) depending on your system design and how fancy a valve they installed.

Answered 2 years ago by LCD

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