Can incorrect balancing cause Boiler Kettling?

[Longclough]

I have a question on Radiator Balancing. Can balancing radiators cause a boiler to kettle if the flow is restricted through each radiator by too much?

Additionally if a bypass valve is closed by too much can casue the same effect. My understanding is that if a bypass is open by too much then the boiler return will be heated more quickly, therefore the boiler will cycle more?

Is my understanding correct?

 

[Agile]

Kind of.

But you dont seem to understand that the bypass is required to maintain a minimum flow through a boiler toprevent kettlying.

Telling us the boiler model would enable more detailed advice.

Tony Glazier

 

[Longclough]

Potterton Suprima 40L
Manual Bypass open 1/4 turn
Pump Set to 2
9 radiators, 3 bedroom radiators with TRV's

Agile thanks for the initial info. Can you explain why minimal flow is not maintained under more operation. I would assume it would since I only have 3 radaitors that will shutdown under normal operation. I assumed that the bypass was mainly required for overrun.

 

[Longclough]

Still trying to understand how much flow should be allowed through the bypass. I have also noticed that when HW is being heated as well as radiators the kettling is much reduced. Can anyone provide anymore info on this problem?

 

[Agile]

Because you cannot measure flow rates in your heating its necessary to get an idea of the flow rate from the temperatures.

Your boiler is designed for a MAXIMUM temperature differential of 11 C across the heat exchanger. You can reduce that if too high by opening the fixed bypass.

Ideally you should have an auto bypass but with so few TRVs that should not be very important if you dont turn too many radiators off.

If its caused by lime scale then adding X200 can often reduce kettling.

Tony

 

[Longclough]

Agile from what you have said, i need to configure the bypass so that the differential between flow and return at the boiler is 11 degrees. what method should I follow to do this. ie all radaitors open, some closed, post balancing or after balancing?

All radiators without TRVs are always left on, as rooms that may not be used are the rooms with TRVs. What ABV still be worth while. Was considering installing once if I drain the system in the future.

I have added X200 which did not have an effect on the kettling, the reason I considered it may have been due to something else

 

[Agile]

Setting the bypass should be done in a typical useage configuration.

Ideally you should have an auto bypass but in your system its not really going to make much difference.

I suppose the starting position would be to measure the flow/return temps at the boiler so you know what you are dealing with.

Then you can balance your system if thats needed. All of these things are interdependent.

Tony