system cannot be balanced correctly?

[bhm1712]

after posting earlier this week i was told my system (although all rads are hot) is not balanced as all the LSV are open. i followed the balancing procedure to the Nth degree.

the difference between flow and return at the boiler with all valves open and boiler on max is 8 degrees. i let the system cool down and shut all the valves including LSV's. previously i had gone around checking in which order the rads heated up and made a list. i started balancing at rad1 and worked around the system according to the list i made.

i achieved the 8 degrees difference between flow and return on each rad, within half a turn on the LSV's.

the problem i get when it is done this way is that the system is so noisy, i can hear the water flowing through the radiators very loudly. after the system is upto temp, the boiler begins to kettle. i can stop the kettling by opening one LSV wide open, which tells me that with the system balanced, the heat cannot escape the boiler fast enough due to the lock shields being turned down so low. the boiler is only on number 3 of 10, any lower and the HW takes ages to heat up.

what is the problem or what am I doing wrong?

Glow worm space saver mk2
Wilo gold on speed 2
22mm main, 15mm to the upstairs rads and 8mm micro to downstairs.
No TRV's (had to remove them because when they closed down the boiler kettled in the same way)
single rads x8 (4 up 4 down)

system is a C Plan open vent.

 

[D_Hailsham]

the difference between flow and return at the boiler with all valves open and boiler on max is 8 degrees.

Was this with the pump set to 2?
Your boiler is designed for a difference of 11°C. What happens if you set the pump to 1?

the problem i get when it is done this way is that the system is so noisy, i can hear the water flowing through the radiators very loudly.

That means the water is travelling to fast.

after the system is upto temp, the boiler begins to kettle. i can stop the kettling by opening one LSV wide open, which tells me that with the system balanced, the heat cannot escape the boiler fast enough due to the lock shields being turned down so low.

Possible mis-match between boiler output and radiator output.

Which Spacesaver Mk2 do you have - there are 17 versions? If not on the case, it will be on the data plate.

the boiler is only on number 3 of 10, any lower and the HW takes ages to heat up.

Not surprising! The boiler temperature must be at least 5°C higher than the required HW temperature.

single rads x8 (4 up 4 down)

What are the sizes of the rads? (height x length in mm)
Are they singles with fins or without fins?

 

[bhm1712]

the boiler is a MK2, 40BR model

the pump speed was speed 2 yes. i will try speed 1 when i am home later!

as for radiator size, i will measure them also when i return home.

thanks for your help so far.

 

[bhm1712]

right i have sizes

2 38x20 inch
1 25x23 inch
1 50x20 inch
3 19x23 inch
1 70x 33 inch

all rads are singles with fins

i have now reduced pump speed to 1 and achieved 11 degrees difference at flow and return at the boiler. i have rebalanced the system to achieve 11 degrees between flow and return on all radiators give or take 0.5-1.0 degree or so.

the boiler is not kettling anymore, but the flow noise is apparent in the upstairs radiators still.

 

[D_Hailsham]

right i have sizes

Thanks for the size info. Your rads add up to approx 7kW.

My suspicion about a mismatch between boiler and rads is correct: 12kW boiler, 7kw rads.

i have now reduced pump speed to 1 and achieved 11 degrees difference at flow and return at the boiler. i have rebalanced the system to achieve 11 degrees between flow and return on all radiators give or take 0.5-1.0 degree or so.

That's good

the boiler is not kettling anymore

So's that.

but the flow noise is apparent in the upstairs radiators still.

I suspect this is caused by the LS valves having to be almost closed due to the high differential pressure across the rads. Fitting an automatic bypass valve would help.

You could also try opening the upstairs LS valves a fraction. It will change the temp drop fractionally, but that's OK.

 

[bhm1712]

thanks for your help and info.

i have noticed that the noise actually gets louder if i crack the lsv's open more than 1/4 turn, then they stay noisy until about 2 turns open, where the noise disappears almost completely.

i had thought that maybe an autobypass might help this. The problem with my system is that it was done cheaply and quickly i guess, when the house was built.