Scaled/Sludged up boiler heat exchanger..........?

[steved101]

I have been reading posts and understand that a scaled or sludged up heat exchanger can cause poor heat output from the radiators in general due to the water in the boiler not getting hot enough, due to the scale/sludge.

How is this so? Surely if anything it would make the water going through the boiler hotter as the scale/sludge in the heat exchanger walls would stop the thermostat / thermistor reading the temperature accuartely and as quickly as it should do?

 

[kevplumb]

it's like lagging the INSIDE of the pipes etc

stops the heat getting in to the water

 

[steved101]

I see, I was thinking of ti from the isnide out.... I understand now, thanks for your reply.

How would this then cause the overheat to trip then (as in some cases it has done).... a if the heat cannot get through to the water.....?

 

[kevplumb]

could well not be even coat all through the h/ex

so if you have a flow restriction say at the return connection the water runs through the h/ex slower therefore gets hotter

 

[mrgas]

If your main heat exchanger is full of crud it will retain more heat than a clean one.
When you stop using the boiler usually after extensive hot water use, this extra retained heat enters the water and can cause overheating and triggering of the stat.

 

[steved101]

i suppose it could slow the flow down in any part of the heat ex and hence cause the overheat stat to trip...?? depending how bad the scale/sludge build up was? The newer boilers have smaller diamteter heat exchangers than the good old cast iron type's used to don't they.


one other thing confusing though - out of interest, a slow flow as you mention would cause the water to overheat inside the heat ex .... but won't the normal stat sense this higher temperatue 1st and cause the boiler to just cycle rather than getting to overheat stat temperatue of say 80-85 degrees?