You say the heating water indicator shows 80C+ very quickly.
This is a sign of low heating water flow through the boiler. I assume the rads are not at 80C, or anywhere near that, because the heating fluid is not being distributed to them. Good advise has been offered. The lack of flow velocity has led to any crap dropping out of suspension at the lowest velocity points - the middle base of your rads! The water you drained may be clear because that crap has dropped out of suspension, but it's still there waiting to attack!
Pump failure or blocked pump? Inspect, clean or replace as necessary, though you can be sure that, if the pump is blocked/choked, restoring its flow will increase the water velocity, picking up lots of this radiator sediment and dumping it...probably in the new pump! Get a Magneclean or similar filter fitted on the return pipe to the boiler to reduce this risk.
Blocked return strainer? Inspect and clean. If blocked it's likely to block very quickly again, for the same reasons as above. Fit a Magneclean, etc.
Other blockage inside the boiler? You'll need a Gas Safe Registered fitter to either dismantle and clean it or, better, locally powerflush just the boiler...then fit a Magneclean...
Incidentally, if the hot water production is OK then it's unlikely to be a blockage inside the boiler, so you're back to the return strainer.
I hope this helps
MM
This is a sign of low heating water flow through the boiler. I assume the rads are not at 80C, or anywhere near that, because the heating fluid is not being distributed to them. Good advise has been offered. The lack of flow velocity has led to any crap dropping out of suspension at the lowest velocity points - the middle base of your rads! The water you drained may be clear because that crap has dropped out of suspension, but it's still there waiting to attack!
Pump failure or blocked pump? Inspect, clean or replace as necessary, though you can be sure that, if the pump is blocked/choked, restoring its flow will increase the water velocity, picking up lots of this radiator sediment and dumping it...probably in the new pump! Get a Magneclean or similar filter fitted on the return pipe to the boiler to reduce this risk.
Blocked return strainer? Inspect and clean. If blocked it's likely to block very quickly again, for the same reasons as above. Fit a Magneclean, etc.
Other blockage inside the boiler? You'll need a Gas Safe Registered fitter to either dismantle and clean it or, better, locally powerflush just the boiler...then fit a Magneclean...
Incidentally, if the hot water production is OK then it's unlikely to be a blockage inside the boiler, so you're back to the return strainer.
I hope this helps
MM
