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The 25-55 180 is the main pump, the UFH has a separate 15-40 130 pump.

I have reduced the output to 25kw, being about 2/3rds the peak output. With that reduction I'm getting a 26c delta between flow and return. In theory if I reduce it to 12kw I should see a 13c delta? Or does it not work like that? I'm assuming it is properly balanced, as it has been working...

Once all the rads are up to temperature, and assuming there is no demand from the UFH and HW, then I assume the boiler will modulate down to its lowest output until the flow exceeds the set point, at which point it will shut down. I don't think this will trigger an S53 though, as the delta...

Hmm. I think I may have been heading up the wrong path here. I've compared the UFH pump to do the main circulator pump. The main pump has quite a bit more noise. The UFH pump just has an electric motor whir. The main circulator has this noise but also you can hear what flowing through it...

Not sure how you should measure this?

1) Yes, the UFH has its own pump. 2) 14 rads 3) 250 litres

Right - on that rule of thumb: 1) Current flow rate = 1.15m^3/hour At 1.15m^3/hr, we know: Boiler pressure loss = 2.0m Rest of system pressure loss = 2.9m 2) Desired flow rate = 1.6m^3/hour Boiler pressure loss = 4.0m (from manual) Rest of system pressure loss = 2.9m * (1.6/1.15)^2...

30°C is the trigger point, this I'm 99% sure about. I've sat in front of the boiler looking at d.40 and d.41 (flow & return temperatures) waiting for it to cut out. It will sit for minutes at a 29c difference, but as soon as it hits 30c differential I think it has 10 seconds to go back under...

I think the Magna can be set up in the same way as an "old-fashioned" pump though? Looking on www.colglo.co.uk, pump prices are: £330 for UPS 25-100 £475 for Magna 25-100 Difference is £145, which would pay for itself much more quickly on the UPS 25-100 versus UPS 25-80. I think if the...

Have just realised I'm wrong on this - based on current performance of the pump, boiler, etc, the system is flowing 1.15m^3/hr. The Glowworm pressure loss graph says at this rate the boiler is giving about 2 metres head of water. Taking the boiler out of the equation and looking at the pump...

With UPS25-80 on middle setting, it uses 155w and will provide 2.2m^3/hr flow at a pressure of 5m. With UPS25-100 on lowest setting, it uses 280w and will provide 3.3m^3/hr flow at a pressure of 5m. The 25-100 looks like it will be overkill, and uses a *lot* more power than the 25-80 for...

Quick online search shows the Magna is £500, and the UPS £200.... Quite a big price difference! Would need to save £30/year on electric, so call it 350kwh, to make the Magna worthwhile.

I've been reading through the spec of the pumps, I seem to have two choices. I want to get about 2.5m^3/hr flow at a 5m head. (To give approximately at 15c temperature differential across the boiler.) The figure for the head is derived from current pump performance graph - see post by D...

It is set at 80c currently. The problem still occurs, even if I lower the flow temperature. Yes, the pump runs whenever there is demand from the heating controls, so even when the boiler is in slow S53 mode, the pump runs. (This rapidly brings down the flow temp from the boiler.) There is...

This is how the controls were programmed - UFC would come on at 5:00am, with the rads coming on at 6:00am. Unfortunately the problem still existed with this - so it's not a case of doing the zones independently will get around the problem.

Yep. Not quite - once the system is up to temperature and the boiler starts modulating, everything is fine. The problem is when the system is coming up to temperature - the boiler on its maximum output causes a temperature differential between flow and return of 30c, which causes the S.53...

Hi Sally, Thanks for your response - I've got another post about the same issue here: http://www.diynot.com/forums/viewtopic.php?t=206079 So I think I'm OK, thanks :) Ed

The fault happens when the temperature difference between flow and return is 30c or more for 10 seconds. The fault happens when the system is relatively cool (e.g. 25c and 55c) and relatively hot (50c and 80c). The 4/5 5/5 output I'm just reading the LCD display on the boiler, it has an...

Yes, I've checked the output of the radiators and there's sufficient capacity there to warrant the 38kw output. I think this is about where my understanding runs out. What is clear is that the 38hxi boiler has a much higher resistance than the 30hxi, and I would imagine the pump has been...

I've just measured the flow to the pump at 26.5mm on external diameter - so I guess is is 28mm and I'm not measuring properly. :)