Pump to replace Alpha2 15-60 130, UPS or UPML?

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I am coming up to my boiler service shortly and I am finally fed up with living with my current Alpha2 15-60 which is too small for my Vaillant 438 boiler. My boiler has been derated to 18Kw.

My plan is to ask my plumber to change my current pump with a new one. I understand the Alpha2 is a 130 so to avoid unnecessary pipe work changes I need another 130 pump.

My options appear to be a UPS or a UPML.
What is the difference between those two?
 
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Will that pump really have more head than my current 15-60. I realise the bore size is greater.
Are you suggesting that Wilo is better than a Grundfos?
 
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So are you suggesting I stay away from the UPS and the UPML pumps?

What's the difference between those two in any case?
 
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What's the difference between [the UPS and the UPML pumps]?
The UPS has 3 fixed speeds. Though the UPS2 15-50/60 also has 3 proportional pressure options.

"The UPML, UPMXL circulator pumps are designed for circulating liquids in heating and air-conditioning systems with variable flows, where the pump is remote controlled via low-voltage PWM signal or internally controlled via AUTO user interface."

Why did you buy a 38kW boiler when you only need 18kW?

What is wrong with the system that makes you think the pump is the cause?
 
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That is a long an sorry story where I listened to advice. Also my house is never being heated all at once, so any total heat loss calculations will result in a larger than required boiler, except in my case no calculations were done at all !
The current pump isn't able to shift the heated water away from the boiler fast enough.
 
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The current pump isn't able to shift the heated water away from the boiler fast enough.
That's probably because the temperature differential is too small. What are the values of d.40 and d.41 when the boiler is working at max (18kW) output?

The 4XX series boilers have very high resistance heat exchangers and are designed to work with a 20C differential. If the differential halves to 10c or 11C the resistance of the whole system increases four times. At 18kw and 20C differential the required flow rate is 775 litres/hour. So the hex resistance is just under 1m, which leaves over 4 metres available from the pump for the rad circuit.

If the differential is only 10C, the flow rate doubles to 1550 litres/hour and the hex resistance increases to 3.7m. At this flow rate the Alpha 2 15-60 has a maximum head of 4m on speed 3, leaving virtually nothing for the heating circuit.
 
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Have a look at the spec and you'll find the Stratos PICO 25/1-6-130 has an almost identical pump curve (performance) to a Grundfos Alpha2, the internal port size of the Stratos is larger but it makes little difference.

Is is not reasonable to run modern boilers with the traditional temperature drop of 11 degrees....a compromise must be made

At only 18Kw output and a sensible temperature drop there should be plenty of residual head left for the system circuit. Are you using the Alpha2 on a fixed speed setting and do you have the auto bypass valve correctly set? (will only need setting to 0.1/0.2meters or so to guarantee a minimum flowrate through the boiler).

Only at the higher Kw outputs should the requirement for a higher head pump be necessary. Certainly at the 38Kw output the Alpha2 will only be sufficient to get the water through the boiler heat exchanger with nothing left for the system.
 
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I don't think my DU144 ABV has been touched. It has been sitting at the factory 0.3 all the while. First of all, would that be the right setting.

First thing in the morning it's only 1 single room that is calling for heat. So the flow temperature rises to the max 60C within about 3-5 mins.

Last weekend I conducted a little experiment and got a lot of the rads calling for heat at the same time. Then the flow took 25 mins to get to the 60C max.
 
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See the temperatures of the Flow and Return during start up. Saturday was when max Flow was set to 70C and many zones calling for heat.
Saturday.JPG

Today was when flow was set to it's normal max of 60C and generally only 1 or 2 rooms are calling for heat, first thing in the morning.

Today.JPG
 
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Have a look in the manual for the status codes....press the i key. See if you're getting an S53 code. It refers to the VL-RL spread which is German for flow and return temperature differential being out of an acceptable range.
Set the pump on a fixed speed setting..probably 2 or 3 and try the bypass at a lower setting say 0.1 or 0.2 bar ie. 1 or 2 meters.
 
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Nope, I get an instant notification for an S.53 and I haven't seen one for a long time. I have spent many months of my life with that S.53 code, in the early days of the boiler install, so know it all too well.

Ever since the boiler was derated to 30Kw, the S.53 hasn't been seen. And now it's derated to 18Kw.

The pump is set to a fixed speed of 3 and the ABV is set to 0.3. If I slow the pump down won't it reduce the flow and cause more of the issues I am seeing?
 
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The UPS has 3 fixed speeds. Though the UPS2 15-50/60 also has 3 proportional pressure options.

"The UPML, UPMXL circulator pumps are designed for circulating liquids in heating and air-conditioning systems with variable flows, where the pump is remote controlled via low-voltage PWM signal or internally controlled via AUTO user interface."

THE UPML AUTO version appears to have 3 Constant speeds and 3 Proportionate speeds, similar to my Alpha2, Hence it caught my attention. Besides it being available as a 130mm model. It is a 25-95 pump. I was not intending to buy the PWM signal driven version. But I wondered why I haven't seen much talk of using this UPML AUTO pump. People mention UPS, Magna and Alpha etc.
 
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