Andrew Gabriel wrote:

In article ,
(A.Lee) writes:
Well, after thinking the combi boiler was fixed, it has started playing
up again.
Alpha 240P, around 10 years old.
DHW runs for 2 minutes, then cuts out for 20 seconds or so, then
restarts, cuts out after a 2 minutes or so etc etc.


I would check to see if the new DHW heat exchanger has got
clogged with rust again. The timing would be about right if
there's still lots of rust in the system.

Well I took it all apart again. The DHW exchanger had around 4 or 5 rust
flakes in it, no more, so attention turned to the primary heat
exchanger.
I tried to undo its connecting pipes, but they were too tight to be
undone, so plan B was to flush it through again.Radiator input tap was
turned off at the boiler, leaving the output tap open, then undid the
drain point at the furthest radiator, then turn on the filling loop pipe
fully, pressure up to 1.5 bar on the meter, and coming out rather fast
from the drain.
This ran for half an hour.
Put it all back together then, and had great difficulty in getting the
pilot to stay alight.
Thermocouple seemed to be ok, so it looked like the overheat themostat
cutting off the gas, took it out, tested it for conductivity, and not a
problem. Put it back with good connections, and it did stay alight
eventually. Looks like the thermostat had a bad connection.

Tested, and found everything working as it should do.
Great.

Now, I've got some Fernox cleaning fluid here. Would it be wise to get
the whole system cleaned again this weekend?

Ta
Alan.

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