Balancing difficulty - perhaps need a second/extra pump??

andyxxx · 24 Oct 2006

I have a 4 year old combi system installed with fairly long 22mm pipe runs feeding several very large double radiators. The BTUs of the rads and pipework are within the rating of the boiler.

No matter how carefully I try and balance the system, I can’t get it right. I can get all the rads to get quite warm (at the same time) – but not all to get 'scorching' hot (at the same time) If I open up a valve on any rad(even a fraction) I find one of the other rads does not heat at all.

I know this sounds strange, but could this be because there is too much water in the system for the pump to cope with?

Would adding a second pump (next to the first, or at a distance from it) help?

Any suggestions greatly appreciated.

Andy

Gasguru · 24 Oct 2006

Tell us the make and model of the boiler.

Are the flow/return isolating valves under the boiler fully open?

There may be a return filter within the boiler - perhaps this is blocked.

Is there a bypass valve between the flow and return pipework under the boiler, if so this may require adjustment.

Some boilers have an adjustable bypass valve within themselves - this may require setting up.

Check the hot water works OK - run a hot tap fully open and check the heating flow pipe doesn't get hot. If it does this would indicate a stuck/partially seized diverter valve - this could reduce heating performance.

andyxxx · 25 Oct 2006

Hi – thanks for the quick response!

The boiler is a Glowworm Xtrafast.

I know little about central heating systems and boilers. The flow/return are fully open and hot water works OK (checked as you suggested)

I can not see a bypass valve between flow and return – perhaps it is within the boiler as you say some are – an area I will not go! I will try and get a pro and also ask if there is indeed a return filter.

If all these things prove ok, is my suggestion of a second pump an option that could cure the problem?

HarrogateGas · 25 Oct 2006

a correctly installed system will need little or no balancing at all.

i suspect the pipwork sizing to the rads to be a t fault.

Steve__M · 25 Oct 2006

If you have one radiator off, do the others all get "scorching hot"?

Have you got your boiler manual? The performance of the pump (in diagram 4 of the manual off the Glowworm website) is dependent on required flow rate of water.

What is the total kW of your radiators? "Several very large radiators" sounds like at least 10kW.

For a balanced system, 10kW (34000BTU) is about 720 l/hour. At this flow, the setting of the bypass has quite a big effect on the available pressure. If it's 15kW your getting towards the edge of the scale.

Gasguru · 25 Oct 2006

This boiler does have an internal bypass that must be adjusted for correct operation.

It appears from the data table the heating output is adjustable however no details are given in the on-line pdf - check your own manual to see if this is actually possible.

It appears the bypass may not be set correctly and the heating ouput may not be set to a sufficient output.

Most domestic heating systems must be balanced for satisfactory operation despite the earlier comments.

Two pipe reverse return (not common in domestic properties), some microbore and some small TRV'ed systems may not require accurate balancing.

andyxxx · 27 Oct 2006

Steve__M said:
If you have one radiator off, do the others all get "scorching hot"?

No, but they get hotter each time I turn another one off.

Have you got your boiler manual? The performance of the pump (in diagram 4 of the manual off the Glowworm website) is dependent on required flow rate of water.

I have now found the manual! I see the diagram you refer to but would not know how to measure the info required to determine the amount of turns required?

What is the total kW of your radiators? "Several very large radiators" sounds like at least 10kW.

I do not know the Kw but at the time of installation I was made aware that the BTUs of the rads and pipework were just within the capability of the boiler. (I seem to remember about 100,000 btus - and can probably find the exact figure)

For a balanced system, 10kW (34000BTU) is about 720 l/hour. At this flow, the setting of the bypass has quite a big effect on the available pressure. If it's 15kW your getting towards the edge of the scale.

I am sorry you lost me here!

Thank you for your responce. From what I can understand here I need to ensure the Bypass is set correctly - and that sounds as if it is going to need to be fully shut?

andyxxx · 27 Oct 2006

Hi

Sorry for the above post – I can’t get to grips using the quote button!

Steve –M

Thank you for your reply

Each time a rad is turned off, the others get hotter until perhaps three or four are off – then the remaining are boiling

I have now found the manual! I see the diagram you refer to but would not know how to measure the info required to determine the amount of turns required

I do not know the Kw but at the time of installation I was made aware that the BTUs of the rads and pipework were just within the capability of the boiler. (I seem to remember about 100,000 btus - and can probably find the exact figure)

From what I can understand here I need to ensure the Bypass is set correctly - and that sounds as if it is going to need to be fully shut?

Gasguru

Thank you for your reply

This is a ‘conventional’ flow and return with trvs to all but one rad (I have removed them when balancing)

Steve__M · 27 Oct 2006

andyxxx said:
I do not know the Kw but at the time of installation I was made aware that the BTUs of the rads and pipework were just within the capability of the boiler. (I seem to remember about 100,000 btus - and can probably find the exact figure)

Sorry I was a bit unclear in my other post. Basically, the more radiators you have, the more water the pump has to pump (the horizontal scale of the graph).

The amount of water happens to be proportional to the total power of the radiators. Because I worked it out on my own system, I know that 34000BTU is about 700 litres every hour hour. So if your system is 100,000 BTU the pump has to push 2000 litres per hour.

If I remember rightly, 2000 litres per hour is a bit off the scale of your graph. So perhaps your original concern:

andyxxx said:
I know this sounds strange, but could this be because there is too much water in the system for the pump to cope with?

may be correct

Be interested to know how you get on with the bypass fully closed.

Gasguru · 27 Oct 2006

Put the heating on (maximum temperature) and run it for 5 minutes. Then go to the gas meter. Measure in seconds the time for the test dial to do 1 revolution. If you have a digital meter measure the difference between the start and end figure over a 2 (two) minute time.

Post the results and we can tell the heating output of the boiler

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Balancing difficulty - perhaps need a second/extra pump??

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