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Grundfos STN 1.5B not right on the hot water side

  • 19-10-2014 1:15am
    #1
    antiskeptic
    Registered Users Posts: 9,555 ✭✭✭


    Have a friend with the above pump doing hot and cold duty in his apartment. The hot side is giving sporadic output: it's slow to produce output when the tap is opened (although pump starts straight away and sounds no different to when it's doing cold water work, which it does fine). Once water starts flowing it's not anything like full force/flow and varies in output (from perhaps 30% of what you'd expect down to 10% of what you'd expect)

    Any ideas what might be up? I gather it's a relatively new pump and he's had a plumber and an 'engineer' out to look at it and they say it's fine (when it patently isn't). Dunno what happened his old pump but it would have been in 12 years if original to building construction.


Comments

  • #2
    K.Flyer
    Registered Users Posts: 8,565 ✭✭✭K.Flyer


    Does it give trouble with one particular tap, or is the problem consistent through all the hot taps and shower valves.


  • #3
    antiskeptic
    Registered Users Posts: 9,555 ✭✭✭antiskeptic


    K.Flyer wrote: »
    Does it give trouble with one particular tap, or is the problem consistent through all the hot taps and shower valves.

    All taps. Thanks..


  • #4
    K.Flyer
    Registered Users Posts: 8,565 ✭✭✭K.Flyer


    Try this..
    Turn on a (good) cold tap on one basin (Not The Kitchen!) and leave it running. Then one at a time check each of the hot taps on the other basins and compare the flow / pressure rates to the cold tap thats still running.
    If the flow is still poor or erratic then there is either a partial blockage somewhere, a problem with the hot supply to the pump or a damaged impeller.
    If the flow is strong and consistent with the cold tap then its probably an issue with the flow sensor or the pressure switch.


  • #5
    antiskeptic
    Registered Users Posts: 9,555 ✭✭✭antiskeptic


    K.Flyer wrote: »
    Try this..
    Turn on a (good) cold tap on one basin (Not The Kitchen!) and leave it running. Then one at a time check each of the hot taps on the other basins and compare the flow / pressure rates to the cold tap thats still running.
    If the flow is still poor or erratic then there is either a partial blockage somewhere, a problem with the hot supply to the pump or a damaged impeller.
    If the flow is strong and consistent with the cold tap then its probably an issue with the flow sensor or the pressure switch.

    Thanks v. much K. Flyer - I'll give all that a whirl this evening.

    Edit: just onto friend to arrange dropping by and it turns out the same pump has been installed in a number of apartments in the same complex and all are having same problem (whereas original equipment runs fine). Case closed as problem is being escalated to the facilities co. who service the building.

    Thanks


  • #6
    nmacc
    Registered Users Posts: 459 ✭✭nmacc


    Sounds like a plastic pump.

    Common problem with apartments. If the pump supplies all of the non-mains water, then the toilet will trigger the pump when the cistern is filling. Water flows through the cold side of the pump, but the hot side is 'dead-heading'.

    The impeller on the hot side will heat up. If the impeller is brass there is no problem, but plastic impellers will soften until the hole in the middle rounds out and the shaft spins without turning the impeller.

    It's a particular problem when there are a couple of toilets and it's worse if they have 'top hat' washers in the ballcocks. These washers harden with age and the fill time for the cisterns will gradually increase, putting more strain on the pump.

    You may be able to get the existing pump repaired by changing the impeller or bringing it out to Grundfos, but I suspect this model may be disposable. Change the washers in the toilet cisterns and then either change to a brass pump, or swap the toilets over to the mains. Not sure if the regs demand a double check valve in the line in that case; I'm sure someone else on here will know.


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