balancing central heating system

[D_Hailsham]

Which pump do you have?

Circulating pumps CP63. previously myson

That should be OK.

The high (25C) differential suggests two things:

1. The head (internal resistance) of the system is very high, or
2. The pump is faulty and not circulating the water fast enough.

When all valves are fully open the system resistance is at its minimum, which would discount the first - unless there was a system design flaw. So we are left with option two.

However, a third possibility is that the valves either side of the pump are not fully open. (Be careful when trying them, particularly if they are stiff; you don't want to break the shaft!)

 

[nairb999]

Which pump do you have?

Circulating pumps CP63. previously myson

However, a third possibility is that the valves either side of the pump are not fully open. (Be careful when trying them, particularly if they are stiff; you don't want to break the shaft!)

I thought about valves. They have not been touched since pump waa replaced 6 years ago. Temp checks across pump ie minimal temp drop.

Can the pump perform differently with hot water passing through it. When I run the system with cold water no problems

 

[D_Hailsham]

Can the pump perform differently with hot water passing through it.

Never thought about it; but I don't see why it should.

When I run the system with cold water no problems

What do you mean by "no problems"? I can't see how you can say that.

 

[nairb999]

Can the pump perform differently with hot water passing through it.

Never thought about it; but I don't see why it should.

When I run the system with cold water no problems

What do you mean by "no problems"? I can't see how you can say that.

I have n't explained myself on this one. If I let the system cool down and then run it with the boiler stat on 0, the pump runs quietly on alll 3 settings. I am coming back to what is probably a badly designed system with no thought about correct order of radiators. Presently I have managed to get 3 radiators working with acceptable noise levels so at least some heat.

I ran the system on just 1 radiator with no noise in the airing cupboard where the pump is located. Took me a while altering the lockshield to achieve this. I have turned on another radiator and adjusted that lockshield till again not too much noise. I now have a 3rd radiator and the noise is just about acceptable. I have left the system like that for several hours on low boiler stat setting and low pump.


So I think I have a system which is going to be very difficult to get fully balanced

 

[wizbongre]

Hi,

Just picking up on your question about the pump running differently with hot vs cold water... As a complete random guess, is it possible the bearings are wearing and the changes in tolerance/load/pressure with hot vs cold water could make the noise change?

Just a thought.

 

[nairb999]

Hi,

Just picking up on your question about the pump running differently with hot vs cold water... As a complete random guess, is it possible the bearings are wearing and the changes in tolerance/load/pressure with hot vs cold water could make the noise change?

Just a thought.

Thanks Gareth. The noise is definetely coming from the 22.5 mm pipes. I think it is turbulence due to improper balancing. Pump is running smoothly

 

[Agile]

Your pump is particulaly prone to low torque caused by the capacitor losing value.

Ideally you should remove head, check impeller is not blocked and then do the finger text ( see FAQ ).

Or you could just remove the capacitor and measure its value if you have a suitable meter. ( Although that still leaves the impeller unexamined ).

Tony

 

[nairb999]

Your pump is particulaly prone to low torque caused by the capacitor losing value.

Ideally you should remove head, check impeller is not blocked and then do the finger text ( see FAQ ).

Or you could just remove the capacitor and measure its value if you have a suitable meter. ( Although that still leaves the impeller unexamined ).

Tony

Tony - The pump only occasionally starts on lowest setting.I can only get it running on lowest setting by starting it on level 2 then switching it to 1. I do have an old pump, might be worth trying that capacitor?

 

[Agile]

That would seriously suggest a low torque caused by low capacitance!

But better to measure the capacitance! The old one may be low too. It seems a particular problem with caps on that particular make of pump.

It can be measured by seeing the current taken from the mains if you dont have a meter to measure capacitance. If doing that its best to have a small series resistance to limit the inrush currect. A filiament bulb is easiest to use.

Tony

 

[nairb999]

That would seriously suggest a low torque caused by low capacitance!

But better to measure the capacitance! The old one may be low too. It seems a particular problem with caps on that particular make of pump.

It can be measured by seeing the current taken from the mains if you dont have a meter to measure capacitance. If doing that its best to have a small series resistance to limit the inrush currect. A filiament bulb is easiest to use.

Tony

Tony, I do have a simple digital multimeter capabable of measuring
volts, dc currant and resistance. So looks like meter is out. Can you give me a little more detail on how to perform other test you suggest and what I should see

 

[nairb999]

I decided to contact Circulating Pumps re my problems and I managed to spend quite a bit of time discussing my problems with one of their technical guys. He repeated a lot of ideas already discussed on this forum but suggested it may not be a pump problem. He felt I had a blockage/restriction which meant the pump did not have enough torque on the lowest setting to turn but on selecting setting 2 that would give a higher starting torque for the motor to run.

So with that in mind I have checked the valves either side of the pump and found the lower valve was fully open or at least came to a dead stop. But with the other valve the shaft just kept rotating. So that could be my problem. I cannot be certain that if I try to close this valve it will actually close so I would like to part drain the system. If I close all the lockshields and trv's on the radiators and bale out the header tank would this leave me with possibility a pint or 2 releasing in the pump area and would I have any refilling issues afterwards.

 

[nairb999]

I decided to contact Circulating Pumps re my problems and I managed to spend quite a bit of time discussing my problems with one of their technical guys. He repeated a lot of ideas already discussed on this forum but suggested it may not be a pump problem. He felt I had a blockage/restriction which meant the pump did not have enough torque on the lowest setting to turn but on selecting setting 2 that would give a higher starting torque for the motor to run.

So with that in mind I have checked the valves either side of the pump and found the lower valve was fully open or at least came to a dead stop. But with the other valve the shaft just kept rotating. So that could be my problem. I cannot be certain that if I try to close this valve it will actually close so I would like to part drain the system. If I close all the lockshields and trv's on the radiators and bale out the header tank would this leave me with possibility a pint or 2 releasing in the pump area and would I have any refilling issues afterwards.

Any help would be greatly appreciated

 

[kidgreen61]

the trick is to bung the pipes in the header tank so that an airtight seal is achieved.

This will allow you to change the iso valves (which sound as though they are goosed) without draining the whole system.

be prepared to lose a small amount of water whilst a vacuum forms in the system.

 

[Agile]

The tech guy would probably never suggest that his pump could be low torque!

I work on systems and can say what is most likely to be the problem!

You need to measure the capacitance or do the finger test!

Tony

 

[nairb999]

The tech guy would probably never suggest that his pump could be low torque!

I work on systems and can say what is most likey to be the problem!

You need to measure the capacitance or do the finger test!

Tony

Thanks again Tony. Now I have to change at least one of the pump valves ( unless it can be repaired ) I will be removing the pump so I will perform the finger test