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Can I replace a WM GV-6 Series 1 boiler with a WM G90+ 6 high efficiency boiler?

dcalbaza Member Posts: 3
Hi all,

I have a GV-6 Series 1 boiler that runs 5 zones and an indirect water heater.
My boiler is getting into the end of life behavior, and I am considering replacing it with a new one.
MW sales recommended a GV90+ 6.
Is the GV90+ is compatible to GV-6 series 1?

For starters, the GV90+ has a secondary condensing stainless steel secondary heat exchanger, which GV series one does not have. For the condensing heat exchanger to work fine, the temperature of the return water must be below 140F, preferable around 100F.

I noticed that in cold winters my boiler works around full capacity, and that the return water temperature is somewhat around 160F, while the boiler produces 180-210F (That is at the end of heating cycle, while at the begining the return is somewhat at lower than 160F). When outside temperature is not below freezing, the return temperature drops a lot, maybe around 80-100F.
Would the GV90+ work fine when the return temperature is around 160F? Can that damage it?

Thank you for your consideration.



  • Zman
    Zman Member Posts: 7,330
    It won't damage it, you just won't get the advertised efficiency at the higher temps.
    It sounds like your existing boiler has an outdoor sensor and a outdoor reset control. The return temps you describe would work well with a condensing boiler.

    That being said, the GV90+ would not be on my list. It is just a Frankensteined GV. It is pretty low efficiency and lacks the turndown ratios of a true mod/con.

    I would recommend doing a heat loss calc rather than replacing like for like. Your existing boiler is likely oversized. Then select a mod/con brand that is well supported in your area.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein