Is draining & refilling bad for the system

[Agile]

Sorry but what part do you need help to understand?

Tony

 

[ZACCCC]

Not sure this is what you mean but you don't need to worry about turning off the cold supply to the combi if all your work is on the heating circuits only.

Thanks Jack but I'm now confused. If I don't turn off the cold supply to the combi then how will I be able to drain the CH circuit? Won't it just keep refilling from the cold supply so it'll never drain? As I say, I'm quite a novice so probably my understanding is all wrong but perhaps you could explain this for me.

 

[Agile]

The CH circuit is totally separate from the cold supply to the boiler which is heated to become the hot water.

But if the CH circuit is drained and water supply left on ( as it usually would be ) then the power to the boiler MUST be turned off.

Tony

 

[St0rmer66]

If the heating circuit is drained you must turn the power OFF to the boiler otherwise it will try to fire up when you take hot water and will be likely to damage the boiler.

Most boilers can be isolated with pressure in them and continue providing hot water.

Most manufacturers will not recommend that though.

Tony

Can you clarify? If CH is drained, a combi shouldnt be used for DHW?

Thanks

You can if the boiler is isolated from the central heating BEFORE you drain it then it will be fine. Or if it's an Intergas. Otherwise no, because it will be empty!

 

[jackthom]

Thanks Jack but I'm now confused. If I don't turn off the cold supply to the combi then how will I be able to drain the CH circuit? Won't it just keep refilling from the cold supply so it'll never drain? As I say, I'm quite a novice so probably my understanding is all wrong but perhaps you could explain this for me.

The cold supply will only refill the CH circuit if you use the filling loop to do so.

You won't have any problem draining the heating but you will need to know how to refill it to the recommended pressure when the time comes.

 

[WabbitPoo]

If the heating circuit is drained you must turn the power OFF to the boiler otherwise it will try to fire up when you take hot water and will be likely to damage the boiler.

Most boilers can be isolated with pressure in them and continue providing hot water.

Most manufacturers will not recommend that though.

Tony

Can you clarify? If CH is drained, a combi shouldnt be used for DHW?

Thanks

You can if the boiler is isolated from the central heating BEFORE you drain it then it will be fine. Or if it's an Intergas. Otherwise no, because it will be empty!

DHW supply comes from the mains water, which wouldnt be disconncted. Sorry - I am not doubting your word, as I am deffo not a plumber, but I DO like to understand how things work

 

[St0rmer66]

The boiler doesn't heat the water directly, it heats the main heat exchanger which has its heat pumped round into the plate heat exchanger which gives its heat to the water via a large surface area inside it. If you drain the system then there's no water in the main or plate heat exchangers and therefore it would either not work or very quickly overheat. Mains water will still flow through the boiler of course but it will come out cold! The boiler needs to be switched off in that case to avoid an overheat situation. If the boiler is isolated BEFORE you drain the system then water will remain inside to be pumped around the heat exchangers and you'll have hot water.