Central heating: What circulation flow rate?

[mickyg]

I'm sure one of the many advocates of viesmann boilers on here, will tell us exactly what the problem is any time now......
personally I still haven't seen one in real life so I can't help in that department

 

[JohnD]

I think they've all flown out to their villas and yachts for the end-of-summer break

 

[namsag]

Bit of a strange job all round first of all johnD has to come on here to ask for them how to get existing boiler off the wall then on again asking about the flue length if it has been left to long .Then a month later it is still not all finished . All a very strange way for an installer to work.

 

[JohnD]

 

[namsag]

John you can nip up to coventry in ten days time and have a word with the viesman bods at there stand

 

[doitall]

(1) the boiler has an error code 0b which signifies air in exchanger, or flow switch faulty, or flow too low

oooh yes he did

I expect it tells me what boiler it is somewhere on diynot

 

[JohnD]

vitodens 100 compact

 

[doitall]

Have you cleaned the spirovent out

 

[JohnD]

yes

there was not much in it, far less than a teaspoonful (the system was powerflushed before fitting the boiler)

as the Spirovent is not a filter, but a settlement jar that stuff falls into as it is swirling past it, it is not liable to cause obstruction by being full.

 

[ChrisR]

Surely the sums are worth doing?
24kW, 20 temp diff

24 / 20/ 4.2 = 0.28 litres/second = about 17 litres/minute

So from

0.5 litres per second (which seems low to me) the pressure drop is about 2 kPa (what's that?)

using 1bar = 10 metres = 100kPa
2kPa is 0.2 metres head.

So 0.28 l/s is just over 0.1 metres, = about 5 inches head

Shouldn't make a fat lot of difference to a 6 metre pump should it.

 

[JohnD]

Thanks for that Chris - you have answered my question!

Not a principle or calculation I am familiar with myself.

BTW @ namsag: the business owner had intended to do it about now, after his summer hols. He had a cancellation and offered to do it in the few days before he went, but hit a problem, hence the puzzling delay.

I am not DIYing it.

 

[ChrisR]

A thought - would the head loss be a lot more if a lot of material had collected? I'm not familiar with the construction.

 

[JohnD]

I have squirted out the accumulated particles

there was not much in it, far less than a teaspoonful (the system was powerflushed before fitting the boiler)

View media item 3783
as the Spirovent is not a filter, but a settlement jar that stuff falls into as it is swirling past it, it is not liable to cause obstruction by being full.

http://www.spirotech.co.uk//popup.php?p_id=129

http://www.spirotech.co.uk/pages/Products/Dirt_Separators/

Sentinel are now selling a thing that appears to be made to the same patents and design

http://www.sentinel-solutions.net/en/waterproducts/systemfilter

 

[D_Hailsham]

but I don't know what "1 m/s" means

One metre per second; that's the speed the water travels. Flow is measured in litres/second; the speed in a 10mm pipe will be higher than in a 22mm as the cross-section area is smaller. If the speed is higher than about 1.5 m/s you will hear the flow and if it is higher than 2.5 m/s the pipe walls will start to erode!

The head from F&E to boiler is about 5m (so about 0.5 bar pressure)

That's the static head. The Alpha+ required a static head of 0.5m at 75°C and 2.8m at 90°C, so you are well within the requirements.

However it is not the static head which is important, it is the dynamic head , i.e the loss in the pipework and radiators due to friction, bends, joints valves etc etc. Have you worked out the index circuit - the one with the greatest loss? It is this, together with the flow rate, which determines the size of pump and the correct setting.

Which Alpha+ do you have and what was you old pump?

 

[JohnD]

15-60 130
when on mid-position automatic, it is much quieter than if you set it to manual II or III

don't know old one. it was a sort of bronze/red colour (!)

an update:

the boss of the firm has been round, he is convinced that the Spirovent is the cause of the problem, tested the output from the flow sensor (it indicates insufficient flow) bridged the sensor and it fired.

So he took the Spirovent off and put pipe in its place...

...still insufficient flow reading from sensor.

With sensor bridged, it heats the rads and cylinder.

He has now ordered a new flow sensor but remains convinced the Spirovent was also obstructing flow...

I'm not sure I believe it.