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Can I turn off domestic water but keep heat on?

seized123 Member Posts: 297
Hi, am going on vacation for a week in January (we live in a cold climate), and would like to turn off the main water supply and well pump, to limit damage if there is a leak, at least in the domestic water circuit. Obviously I have to keep the heat on. Is this okay?
It is an hydronic baseboard oil furnace system (Weil McLean furnace). I’m assuming that the heating part, as opposed to the domestic water part, is generally a closed system, getting replenished only if the pressure drops, and that it would rarely need replenishment? If so, would a week with main water off but heat on be okay? I don’t think I have a low water cut-off valve, though I’ll research more what they look like.
The only problem I can see is if somehow the heating system lost pressure due to a leak (does it lose pressure in normal use?) and the furnace kept operating. I could see this happening if we lost power, the heating pipes burst, power came back on and the furnace did its thing again but with no water to heat.
It occurs to me that instead I could possibly leave the well pump on and cut off only the domestic water, leaving open the feed to the furnace - I might have the valves in place to do this. Then if there was a leak anywhere before the domestic cutoff it would flood my basement, but not the rest of the house.
So, should I: 1) turn off well pump and main water but leave heat on, or 2) leave well pump on and cut off only domestic water, if I can, allowing replenishment of heating water, or 3) leave everything on, in which case a leak in domestic water system would be pretty disastrous. (Going away in warm weather I sometimes turn off everything, heat and all.)
I have always wondered about this, what would you advise. Many thanks in advance.


  • seized123
    seized123 Member Posts: 297
    I should have checked this before, but it appears I can’t shut off domestic water only and still have water go to replenish heating circuit, so it’s all water off or all water on.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    edited December 2022
    Normally I would say YES turn off the water. There is a small possibility that the Weil McLain will loose pressure and fail to maintain heat. SMALL possibility. What is the down side. The pipes freeze and you loose the water in the heating system. That is better that if the water was left on and the pipes freeze. the water feeder would keep feeding water to the broken pipe in the heater and the problem would be much worse when you returned.

    In order to insure against boiler water pressure dropping during extended time away with the main water feed closed, you could add a bladder tank to tour system. This is the tank used when people have Well water for there home. If you had a 30 gallon tank in the system, and you shut off the main water supply to the house, the plumbing system would have that 30 gallon reserve to use while the main was off. That should be more than what your Weil McLain would need for a few weeks with the water main turned off. The left illustration might be a typical home like yours. The illustration on the right shows the 30 gallon bladder tank. With the water main valve closed there is a 30 gallon reserve under pressure. If there is a leak, the most that can leak out is that 30 gallons

    If you wanted to protect and feed water ONLY to the heating system, You might elect to place the bladder tank just after the manual shut off to the boiler and before the Pressure Reducing Valve (PRV). This way when you shut off the main to the house, you also shut off the manual valve to the boiler feed line. Now if there is a leak in the house lines, the bladder tank will not back feed up into the leaking pipe(s). The bladder tank will only feed water to the boiler closed system, in the event the pressure drops below 12 PSI on the boiler gauge.

    I hope this clear...for your review, At least as clear as mud, anyway

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 9,850
    I would shut off the feed to the boiler now and see if it holds pressure over a week or 2 to make sure the system isn't leaking then decode from there what your best option is.
  • seized123
    seized123 Member Posts: 297
    Fantastic comments, thank you!
    Ed, between the well pump and the main water cutoff I have a Pentair Wellmate WM-9 pressure tank, 29.5 gal capacity. So, I could turn off the well pump and leave the main cutoff open and the 30 gals would be available if needed? Sounds like a plan. Although then I couldn’t open the faucets and drain the water like I see some people suggest (but I’ve never done that) but even if that made the pipes more likely to burst if we lost power or heat, the immediate damage would only be 30 gallons. And I’m getting a remote wi-fi temperature alert thing, so if I see a drastic drop I can ask someone to come in and shut the main valve off. Plus, I’ve been reading that it takes a lot of sub-freezing weather to freeze pipes.
    mattmia2 I will definitely do that. The gauge reads 10 psi now, but my plumber told me he hooked up his own gauge and it’s really higher (he’s retired otherwise I’d ask him all this).
    If I don’t see a big drop in a couple of days, I might just end up turning off main water, since as you say Ed the chances are small.