How to mend Vaillant Mag 325

Hot water comes and goes!?

how to fix water pressure its down at bottom of grey part?

What does f.25 mean?

Vaillant 828E - no hot water?

Boiler over pressure on the hot-water side?

Valliant Eco tec 28?

Vaillant Thermocompact Fault?

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Valiant thermostat , BMU-Err ?

No hot water, intermittent when air temp drops?

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How do I fix f22 error on my Vaillent Ecotec Plus boiler?

can i replace my Potterton EP2 2 way programmer with a Center EHE0200361 RF?

vaillant ecoTEC plus boiler fault code - how to fix?

Vaillant ecotec plus 630?

Why is heating on at night?

Problem with the pressure in combi boiler?

Vaillant eco plus 531 boiler?

my boiler will no work?

Vaillant igniting issue ( domestic ) not CH?

my vaillant boiler is saying a code com on it ?

Vailliant turbo max plus 824e?

Vaillant Ecotech Plus 831 F22 fault?

Vaillant F22 fault?

how do I vent the heat exchanger?

Advice?

how do I rectify the fault as detailed below?