Flow rate in central heating system

[edb49]

Thanks for the comprehensive & thorough response, all makes sense now. Will get the pump on order and fit it ASAP.

 

[D_Hailsham]

Plus the instructions state any pump must be set to it's highest speed thus infering fixed speed pumps not modulating.

They do not say that.

All they say is:

A variable duty pump should be set to give a temperature difference of no greater than 20°C between the flow and return, with the thermostat set at “MAX”, which is about 80°C, to give a flow rate as given in the table.

A Magna is an "infinitely variable duty" pump.

 

[Biggles..]

Dh can't fault your technical knowledge but have you actually ever fitted a magna(upe) or an alpha to this product or similar group product.

For ref, you wouldnt fit a 32mm port pump to the size pipe work you have as the 28mm is then the restriction.

Port size 25 is for 28mm pipe, you could down size ie 35mm pipe with a 15mm port pump but you wouldnt have bigger port than pipe.

 

[Biggles..]

Plus the instructions state any pump must be set to it's highest speed thus infering fixed speed pumps not modulating.

They do not say that.

All they say is:

A variable duty pump should be set to give a temperature difference of no greater than 20°C between the flow and return, with the thermostat set at “MAX”, which is about 80°C, to give a flow rate as given in the table.

A Magna is an "infinitely variable duty" pump.

You are quite correct sir,appolagies, i stand corrected.

 

[Agile]

Dh can't fault your technical knowledge but have you actually ever fitted a magna(upe) or an alpha to this product or similar group product.

DH is an armchair expert and not an installer. But I am impressed by how well he does without the practical experience.

I prefer to use a lot of practical experience as theory and reality dont always match well. As in gas pipe sizing where the measured resistance can by up to twice the calculated value.

We can measure temperature and boiler input power very accurately but we cannot normally measure flow rate directly.

Tony

 

[edb49]

OK, glad to say this is all resolved now. Fitted a UPS 25-80 180 pump (230 volt version) and on its maximum output this has brought the maximum temperature delta down to 23c on the boiler.

(Took a week for the pump to get delivered, just fitted it this evening.)

This is marginally outside the range for the boiler, but importantly it doesn't reach a 30c delta and trigger an s.53 code.

Heating controller can now be programmed to turn off heating at night!

Thanks to everyone for all their input into this thread, it's been really helpful, and very much appreciated.