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Temporary boiler bypass - do I need it?

Henryk Member Posts: 1

I bougth a house and am redoing the heating system from baseboards to myson radiator panels with homerun manifolds

I need to disconnect the current supply and return pipes from the boiler so that I can remove the old pipes and run new pipes (pex). This will take me probably more than a month to do so (diy).

My question is about what I can do with my boiler in the meantime. The boiler is the weil-mclain oil burner that is a combo boiler and tankless water heater. I need the tankless water heater to work but do not know if I can just shut off the valves for supply and return for the boiler's radiator piping.

Or do I need to create bypas loop between supply and return on boiler?

There should be water still in the boiler, except it won't be able to circulate

The model of my boiler is weil-mclain wtgo-3

If the thermostat is in off setting , teoretickly the boiler should not go on, only the tankless heater.

The quick question is:

Can I just shut off the supply and return valves on boiler's radiator pipes and then cut the pipes. Leave that cut until I am ready to reconect supply and return to the new manifold. Or do I have to create temporary loop between the supply and return for the time period? The work will take me probably about a month, so the boiler water would be not circulating for that long.




  • Alan (California Radiant) Forbes
    The quick answer is:


    The slow answer is:

    You don't need to create a by-pass as long as you disable the pump.  It would be the same situation as when there is a call for DHW during the summer when the heating is off, no?

    But please check with others.  I don't see many tankless coils in this part of the country.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • ChasMan
    ChasMan Member Posts: 462
    edited June 2010

    I would just bypass it for what it takes to keep the system sealed. You can leave the valves closed but valves have a tendency to leak. Your boiler will be under normal pressure if you have a coil making hot water so the last thing you want is a leak. If you do decide to not do the bypass make sure you disconnect the pump. You really don’t want to pump against closed valves. It will ruin your pump and could make a big mess. Also, be careful, that water is hot. make sure you know how all the valves in the system work and the possible impacts of opening and closing them and what happens if cold supply water suddenly rushes in or if the system runs dry.
  • Tim McElwain
    Tim McElwain Member Posts: 4,628
    The tankless is a seperate water system entirely

    as long as all the electrical safeties are operable it will work as you stated. Just insure that the expansion tank is still in the system of the boiler. Make sure you plug both sides of the piping to insure the boiler system remains a closed system.

    I assume you are a homeowner so it may be a good idea to have a pro take a look at it and give you first hand advice at the site, better safe than sorry.
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