Saunier Duval Themaclassic F30E Combi

[shalien]

I have a 4 yr old Saunier F30E standard combi running on natural gas and the hot water is failing dismally. However heating works AOK.

Symptoms-

turn on hot water, boiler fires, flame spreads across whole burner, burns for about 10 seconds, goes out, 15 or so secs later flame re-lights, REPEAT

Items checked so far-

cleaned boiler as per installation manual.

set sensor electrode and ignition electrode gaps to 3.5mm as per manual.

measured voltage at H2 from flame sensor electrode, result 6 volts when flame covering electrode.

disconnected flame sensor, result, lockout with fault code F1 shown on display.

measured voltage across all 3 leads of flow sensor. result 6-7 volts across each terminal.

Checked Control board PCB, no sign of dry joints on soldering. resistors appear to measure OK.

BTW, I am a sparky, and have serviced this boiler regularly plus flushed system and used inhibitor, 18 months ago replaced three way valve actuator and diaphragm, both still working and A1 condition.

Any Saunier experts with ideas of a fix, (don't much fancy paying £150 for new PCB)

TYIA

 

[zk]

seems as though the plate heat exchanger is blocked.

 

[shalien]

Is that the one behind the three way valve, or above the burner?

 

[zk]

behind the 3 way valve.

 

[shalien]

not tried that one, what are the generic symptoms of a blockage there then?

 

[twgas]

a little hot water - a little cold water - a little hot water......................

 

[shalien]

I'll have to try that that at the weekend. Looking at the boiler schematic, i asume this wouldn't affect the flow sensor or does it? Any experience of removing this to flush, whats the easiest way? and hows the best way to flush the exhanger. Am I right in remembering when you remove the three way valve and the domestic HW the exchanger will just come free or is it attached in some other way to the boiler housing?

is it as easy as item no. 20.32 on page 54 and item 20.34 on page 55 on this link- http://www.saunier-duval.co.uk/manuals/pdf/current_products/installation_ThemaF30e.pdf makes it out to be?

 

[shalien]

Sorted it. just finished!

Stripped the boiler tonight, DHW Plate to Plate exchanger was well clogged. used a pack of kettle descaler, good flush thru' works as good as ever now.
I will be treating it with Fernox system flush tomorrow, then fernox inhibitor, instead of the cheap stuff.
anyone got any objections to that?

all the best

Shalien