Vaillant 242EH intermittant hot water

[Vaillant242EH]

Hello All.

The CH output is working fine comes on as required, but the HW does not always fire up on demand. I have good water pressure. Often (and this is very annoying in the morning) the HW will not heat up and just runs cold. I can sometimes get HW by turning on the CH, but when the CH up to temperature, the water goes cold and the HW light has not switched on.

I have already searched the site and found that the servo valve or diverter valve may hold the answer to the problem.

Trouble is, the installation manual doesn't refer to a "servo valve" and doesn't explain how it all works. Can someone please explain how it works and suggest a remedy?

Thanks in advance.

 

[Gasguru]

The boiler does not have a DHW demand light just a demand light for heating or hot water...are you sure you have the correct model number...does it have square pressure/temperature gauges.

Have a look under the boiler - the circular brass lump in the middle at the front is the water section. When you turn on the tap a pin in the top of it moves up, rotates a cam and operates the DHW switch. Check if this is happening.

 

[Vaillant242EH]

Thanks.

It has a round temp/pressure gauge and separate lights for DHW and CH. Checked again, the manual is for 242E.

 

[Gasguru]

Turbomax then...black panel and green knobs.

Hinge down the controls panel and have a look on the right just below the pump.

When the hot tap is opened the small white lever (the bow) should move downwards and activate the microswitch. If it doesn't move the diaphragm (in the lower part of the diverter) has failed or the bow has snapped. Sometimes the microswitch just requires a little adjustment with the screw above. Sometimes the lever actuates the switch but the contacts have failed.

 

[Vaillant242EH]

Thanks. I have found the right bit (not easy to see stuck behind the pump as my boiler is in a corner). Well, sometimes the lever moves and actuates the switch when I run the hot water from the tap, and sometimes it doesn't. What puzzles me is why it works some times and not others.

Any (more) ideas all gratefully received.

 

[Gasguru]

Probably a failed diaphragm...you can get a kit but won't be an easy job if the boilers stuck in a corner on the right. Might be easier to change the whole diverter valve.

There is a little adjustment on the switch that may get it going for now.

 

[Vaillant242EH]

Thanks for the useful info. I'll take a bit of time with it and see what I can do. Any recommended links/shops that sell diverter valves?

 

[namsag]

01772702755 gas appliance spares next day delivery diaphragm less than tenner whole valve about £120 to public also tube of silicone grease req to smear orings otherwise they will prob leak

 

[heatingman]

WARNING!!, When you remove the three pump retaining screws make a note of where they come from, different lengths. If you ram the wrong one home you will drill a beaut of a hole into pipe behind. Last comp i worked for they used to do it all the time.

 

[Vaillant242EH]

WARNING!!, When you remove the three pump retaining screws make a note of where they come from, different lengths. If you ram the wrong one home you will drill a beaut of a hole into pipe behind. Last comp i worked for they used to do it all the time.

OK!! Noted!

 

[Whiter]

Get the manual it will tell you how to remove the diverter valve, a set of new O rings might help especially the ones for the pump.