John G you are a star!!! Set the pump to PP2 and all is sweet! I thank you sir.
Would you mind spending 2 mins explaining to me in laymans terms exactly what the Proportional Pressure setting does? It must be more that just a lower pressure setting - thanks.
Good to hear that the pump over has stopped, I assume that you checked it with CH only & HW only. One concern I have is that you may have a partial blockage of the boiler heat exchanger as you ran for years with no pump over on a fixed speed setting, if there is a blockage and it gets progressively worse the the pump on PP control will just keep modulating down and the boiler deltaT will keep increasing for any given firing rate, I think some boilers cut out if the deltaT exceeds 25C or 30C, on the other hand you may have no blockage and/or you may have cleared it out with the chemical addition. Pump PP control is not recommended for boilers with a ABV (auto bypass valve) which opens on circ pump over run (if installed) for a short time on boiler shutdown to remove the residual heat from the exchanger, this is no problem with a fixed speed pump as the pump head will rise to its max (4M in your case) when all the zone valves shut so th ABV can be set at say ~ 3M so that it will open only on boiler shutdown, On PP control, the pump will reduce its speed to maintain its minimum head of ~ 1.2M but if you set the ABV down to say 0.8M then when the boiler comes back on the pump will ramp up to maybe 2M or so and there will be excessive bypass at this pressure. Again your boiler may not be fitted with this or it may use the post air purge to cool down the exchanger.
Now for the good news....pump PP control.
PP control was introduced on A rated circ pumps to save energy and in some cases to reduce noisy TRV,s when throttling down.
I have one myself (Wilo) which consumes 21/23 watts with everything opened up and falls to 12/14 watts on CH only when some of the TRVs are throttled down.
They work like this, depending on the PP setting you select the pump then sets a minimum head at zero flow and a maximum head at its full flow. For example assume that PP3 setting is selected on the UPS2, at that setting (see page 11 of the manual), the pump will modulate between 0 flow at 1.2M & 2.15M3/h (36 LPM) at a 3M head.
Now assume that the pump is running on fixed speed1 and the system with everything opened up requires a 2.9M head at a f/rate of 0.9 M3/h (15 LPM).....you now change over to PP3 control, the pump will go minimum speed and then starts ramping up, for any given point on that "curve" the pump calculates the exact power needed and compares this with the actual absorbed pump power and because there is only one point on this (or any) curve where that calculated power and the absorbed power are exactly equal then the pump will stop ramping and remain at this setting until the system conditions change. I am able to calculate this in a spreadsheet (unfortunately that I am unable to post on here) so if we go back to our original requirement of a 2.9M head at 15 LPM and c/o to PP control then the pump head and f/rate will fall to 1.8M head & 11.6 LPM, as the system requirements fall then the pump will modulate still further. Again if you are back to fixed speed and you shut off "1/2" the rads you might need a 2M head for a f/rate of 7.5 LPM, change back to PP control and the head will fall to 1.52M & the f/rate to 6.7 LPM. If you "dead headed" the pump by say shutting the pump discharge isolating valve, the pump head will fall to 1.2 M at zero F/rate, if you fitted a controllable by pass around the pump and started opening it, the pump would ramp up to a 3 M head & a f/rate of 2.15 M3/h or 36 LPM.
Edit: Should have asked, what PP setting are you using??, thanks.
Have just seen that you are on PP2, I will adjust the numbers above shortly to reflect this, I would suggest PP3 if still no pump over.
I have left the above PP3 and shown the PP2 settings below, very little difference, one of the draw backs of UPS2 PP control.
PP2 SETTING
assume that the pump is running on fixed speed1 and the system with everything opened up requires a 2.9M head at a f/rate of 0.9 M3/h (15 LPM).....you now change over to PP2 control, the pump will go minimum speed and then starts ramping up, for any given point on that "curve" the pump calculates the exact power needed and compares this with the actual absorbed pump power and because there is only one point on this (or any) curve where that calculated power and the absorbed power are exactly equal then the pump will stop ramping and remain at this setting until the system conditions change. I am able to calculate this in a spreadsheet (unfortunately that I am unable to post on here) so if we go back to our original requirement of a 2.9M head at 15 LPM and c/o to PP2 control then the pump head and f/rate will fall to 1.58M head & 11.1 LPM, as the system requirements fall then the pump will modulate still further. Again if you are back to fixed speed and you shut off "1/2" the rads you might need a 2M head for a f/rate of 7.5 LPM, change back to PP2 control and the head will fall to 1.35 M & the f/rate to 6.2 LPM. If you "dead headed" the pump by say shutting the pump discharge isolating valve, the pump head will fall to 1.1 M at zero F/rate, if you fitted a controllable by pass around the pump and started opening it, the pump would ramp up to a 2.7 M head & a f/rate of 2.34 M3/h or 39 LPM.