potterton suprima, boiling + lock out

[Simon F]

about 6 months ago I looked at this boiler, customer said the pipes were banging and then cut out.
assumed pump was sticking, reset boiler turned on tested pump seemed ok, left it at that.

today had same issue, boiling and cut out. pump was 6m on setting 3!
all I had was a 5m so I fitted it set it to 2 and turned on.
within a couple of minutes rattling, turn pump to 3 improved but after a while rattling again.
So I refitted the 6m pump, turned on and it was ok for the rest of the time I was there.

It's a cast iron heat ex, is it likely to be clogged and restricting flow enough to cause the problem?
boiler is about 18 years old.
magnet on the pipes gave no indication of blockages.

I have left it as is, with the suggestion of a new boiler or possibly a chemical treatment and see if it improves. system is 10mm copper to radiators, but the issue has been with the hot water only.

Am I missing something obvious? would you be thinking blocked hex?

 

[gasmanrob]

Definitely piped up the right way?

 

[Simon F]

yes pump flow up to 3 port valve.

it's been in 18 years, only an issue recently

 

[Simon F]

thought just occured to me, there was a balancing valve for the hot water.
I will have to call back try the pump at speed 1 through the radiators,
if that's ok it's not the hex.
then I will be looking to check the valve has not over time got furred up,
try opening it a tad and see what happens.

 

[Elgordo]

If pump is good then blockage most likely in those 10mm pipes , I would try DS40 or equivalent for a few days and a mains flush .

 

[Reg Man]

Blocked cold feed where it enters the flow?