Technically satisfied when using the unistor in this case but it makes no difference which manufactures unvented is used, belt and braces being 240 volt to boiler/VR being supplied via unvented thermal cut out.
The 15/60 that has been installed on the ground floor zone is 'robbing' (laymens terms so it is understood) any head/flow available from the 15/50 in order to circulate water through the upstairs zone (when both calling for heat) , it has been said umpteen times the circulators must be installed in series BEFORE any zone valves , either remove the 15/60 and install it downstream of the 15/50 or simply remove both circulators and fit a 25/80......................or leave the circulators in situ and install an additional 15/60 to first floor zone.
Could you explain a little more on the term "robbing" please ? I've now purchased a Grundfos 25-80 (not the MAGNA1 series, but traditional fixed speed). As an aside, there seem to be multiple versions of this pump, as some have a head of over 8m, whilst others (the one I have) the graph shows a head of max 7.5m.
I intend on replacing the 26-50 with the 25-80, but want to leave the additional d/s pump in place, as removing this would involve draining down the system and pipework. Can you tell me if the problem of the d/s robbing the u/s remains with the bigger pump, and if so, what the reason behind it is ?
I've also been using my flow and return temps to try and "calculate" what my head is, using the pump graphs. For the single pump u/s, this is fine. Is there a way of calculating this for the two pumps in series d/s ? Is it as simple as adding the head together for the two pumps at a given flow rate (flow rate calculated by delta T) ?
If you have two circulators in series to one zone and a single circulator to the other zone and both zones can be used independently or both together then one set of rads can never be balanced correctly depending on what zone is in operation.
Not too clever the second circulator. Who's idea was that?