Old pump in Combi was running slow and overheat stat was cutting burner off in DHW and CH. The downstairs rads were cold and upstairs rads just getting warm.
New Grundfos pump fitted has restored the DHW but the CH is not improved and boiler cycles.
When the CH is turned on, hot water flows down to the 1st floor initialy (boiler in attic). But after about 1 minute the auto by-pass in the boiler opens, returns the hot water back to the main heat exchanger and causes the CH stat to turn the burner off.
Following a suggestion on another post of a potential blockage, I have flushed the system using the fill loop at the boiler.
By closing the CH flow isolation valve under the boiler I can get a good flush down the return pipe, through the rads (5 mins each in turn) and out the drain-valve which is next to the TRV on the kitchen rad.
However, closing the CH return and opening the CH flow means the water is now going through the main heat exchanger etc before going down the flow pipe and out the drain. Result is a much smaller amount out of the end of the drain hose.
Definately a blockage in the flow pipe somewhere ?
New Grundfos pump fitted has restored the DHW but the CH is not improved and boiler cycles.
When the CH is turned on, hot water flows down to the 1st floor initialy (boiler in attic). But after about 1 minute the auto by-pass in the boiler opens, returns the hot water back to the main heat exchanger and causes the CH stat to turn the burner off.
Following a suggestion on another post of a potential blockage, I have flushed the system using the fill loop at the boiler.
By closing the CH flow isolation valve under the boiler I can get a good flush down the return pipe, through the rads (5 mins each in turn) and out the drain-valve which is next to the TRV on the kitchen rad.
However, closing the CH return and opening the CH flow means the water is now going through the main heat exchanger etc before going down the flow pipe and out the drain. Result is a much smaller amount out of the end of the drain hose.
Definately a blockage in the flow pipe somewhere ?