Grunfos UPS 2

Discussion in 'Plumbers' Talk' started by Devil's Advocate, Aug 9, 2017.

  1. Devil's Advocate

    Devil's Advocate Well-Known Member

    For gawd's sakes...

    Thought I'd do a surf for 'pulsing' UPS2, and it seems it's (a) quite common and (b) a fault...

    Looks like these electronic jobbies are sensitive to electrical spikes and sh**.

    So it looks as tho' I'll have to replace the 3-porter, PCB AND the bludy pump!


    Something I don't understand about these pumps - you can set it to 3 fixed speeds like a normal pump, but you can also set them to 'proportional pressure' in each range. Ie, it'll spin as fast as needed, but will slow down when TRVs shut off and less flow is required.

    Cool. BUT, why would anyone set it at a fixed speed? Surely 'variable' is always the way to go? But there's no advice on this given in the instructions - it just tells you there's the option.

  2. MGW

    MGW Active Member

    I asked the question "How does the boiler know when all the TRV's have closed?" it would seem from answers this varies, when all TRV's close the by-pass valve should open and hot water returned to boiler, with some boilers the by-pass valve is internal so it could have a micro switch on the by-pass valve, but my attempts to find out which boilers do what failed.

    The theory told to me years ago was the boiler has anti-cycle software, when demand is satisfied the boiler switches off, after a pre-set time it tries to fire up, if the water after it fires up is still hot then the pre-set time is increased, if not then time is decreased.

    Where it all goes haywire is when you have radiators without TRV's fitted, it would seem there must be so much coolant that can pass or so much temperature drop, however hunt as I did I could not find out how much.

    I am sure in my mothers case it is too much, as the cycle time does not seem to alter, it seems the way the anti-cycle software works is a big secret. Even the boiler manufacturers say have one radiator without a TRV fitted, so one can never have all radiators off, I struggled for ages to get the central heating to behave.

    In the end I did what it says don't do, I fitted a TRV in the room where the wall thermostat was, it worked. So if the fixed speed allows the anti-cycle software to work, that would explain using it.
  3. Devil's Advocate

    Devil's Advocate Well-Known Member

  4. sam spade

    sam spade Active Member

    I assume you are talking about a modern modulating boiler.

    The boiler will modulate (adjust its output) to keep a constant flow temperature. As TRVs close less heat is required so the boiler modulates down to maintain the flow temperature. If the boiler has reached the lower limit of modulation it will go into on/off mode and anti-cycle will take over.

    As for the fixed speed feature on the UPS2, I have one of these pumps, fitted last year, and have kept it on fixed speed 1 as I'm not convinced it will give sufficient flow when set to a variable speed. I know I could give it a whirl, but don't like the possible consequences if the flow rate is to slow.
    MGW and Devil's Advocate like this.
  5. MGW

    MGW Active Member

    I realise that, to condensate the liquid in the flue gases the return water needs to be cool enough, however there also needs to be a minimum flow rate, or before it leaves the pre-heater it will get too hot.
    This is the main problem, we don't know, there is just a lack of information on what the boilers need.

    What I need is to do some monitoring, I don't have a smart meter, however I do have a pet cam which I could set up so I can actually see the gas meter, it would be easier with a meter giving direct kW being used, but I need to wait until winter.
  6. sam spade

    sam spade Active Member

    What pre-heater are you talking about?

    The minimum flow rate specified in Tech Specs is that required to give the maximum permitted temperature differential (normally 20C) across the heat exchanger at max output. When the boiler has modulated down to minimum output the flow rate can be proportionally lower for the same differential.

    What are you trying to find out by monitoring the gas meter?

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