For the past 4 months I have had intermittent hot water with my Vaillant TURBOmax VUW 242E, well rather luke warm. The central heating seems to be okay. I have had an engineer in and he changed the diaphragm and changed the pressure in the boiler (I assume water) and it seemed to work for about 5 days, but it's getting progressively worse again now. When the heating is on first thing in the morning and someone runs the hot tap the boiler lights go mad, the lights jump from water to radiator to ignition indicator to flame to burner lock out, this keeps going on until finally only the water and flame are lit. During the day, more often when the heating is off you don't get any response from the boiler, it just runs cold water.
I have spoken to my engineer again and he did suggest it sounds like the diaphragm again or the water pressure, but I can't see it being the pressure as it's up higher than we use to have it before the problem arose, can someone tell me what the problem is?

Julie, March 2008

just done this job on my boiler the diaphragm was fine but found that rust in the system had not ceized but slowed the working parts so drain the boiler strip out diverter valve and flow switch and completely strip down and clean down all moving parts removing all rusty or slimy deposits and re grease with a silicone grease and also test micro switches with mulitmeter with continuity test. Before doing this i would buy new seals for the water pump, heat exchanger and the diverter valve using old seals never works out well. also i would buy some system cleaner and give the heat exchanger a nice overnight bath in it along with the small copper pipes and sometimes the flow switch can need readjusting. its a lot of work and quite messy but worth doing the whole lot in one go than going back two months later and definately get some system cleaner in your system followed by inhibitor say a week later depending on the age of your system.

good luck

matt gillingham, June 2012

try draining the system down and remove a component called aqua sensor connected to cold outlet which senses the flow it can get blocked up causing the sensor not to pick it up.

Gasman, August 2010

if the boiler is not firing up and the diaphragm is good and fitted correctly then the problem could be your diverter valve of the micro switch on the side of the diverter.
the cheapest is the switch, but most likely the diverter itself.

gary.wright53@googlemail.com, March 2008