Hi,

I have a problem with a Ravenheat CSI 85 (18 months old) which will only give DHW when the CH is on.

If turned to DHW mode the boiler will not fire.

I have checked diverter valve which is operating microswitch ok when hot water tap is running and also checked that microswitch works and leads back to circuit board are all ok too.

There is allot of corrosion(water dripping) around the DHW thermistor - could this stop the boiler firing up?

Also, this might be a separate problem but sometimes the heating comes on without being asked for but only for a little bit, the radiators get luke warm then boiler stops - i have had a look at the diaphram but it looks ok(i think?)

Any ideas summers coming and having to turn the heating on to warm the hot water is driving me mad!

thanks,

Louis

Louis, February 2007

I have exactly the same problem. Changing the DHW thermistor fixed it.

Ski, December 2016

Here's another Ravenheat CSI 85 tip. The combustion chamber has a pressure switch and this will only operate if the chamber is sealed properly. In particular there are gaskets (silicone I think) on the gas inlet pipe and the condensate outflow. If any air gets in the boiler won't operate. Check all the other places where pressure might be lost e.g. the fan fitting and gaskets where appropriate. Incidentally I've seen these boilers supplied with the condenser not screwed down at all, just sitting on the inlet pipe compression joint. This causes the pipe on the very heavy condenser to "sit" on the gasket cutting through it against the casing. The fibre washer on the condenser compression joint can fail catastrophically too because of the undesigned twisting force from the condenser. The condenser is drilled for a self-tapping screw to pass through and into the hole in the casing. I assume the assemblers didn't try using the screw and I can see why. The build was poor - the hole mis-aligned and I've found myself finishing off assemblies by drilling another hole for the screw.

Edward James, April 2011

I'm surprised that fixed it. That corrosion around your DHW thermistor is caused by water weeping from the joint which wasn't tightened properly at the factory (2003/4 models -& later?). The water eventually rots through the thermistor connections, and it normally goes open circuit. This causes the DHW to run at FULL HEAT, and you may hear the boiler 'roar' more than usual. P.S.The CH thermistor is often undertightened too...

viridens, October 2007

That corrosion around your DHW thermistor is caused by water weeping from the joint which wasn't tightened properly at the factory (2003/4 models -& later?). The water eventually rots through the thermistor connections, and it goes open circuit. This causes the DHW to run at FULL HEAT, and you may hear the boiler 'roar' more than usual. So this is not your problem here. P.S.The CH thermistor is often undertightened too.

viridens, October 2007

The new temp sensor fixed it!

-thanks for your help!

Louis

Louis, February 2007

Thanks The Gas Man,

Your advice *greatly* appreciated - I will get a new thermistor tomorrow.

Sorry if this is a silly question but is 15-20 k,ohms when the thermistor is hot or cold?

Anyway will post the results.

thanks,

Louis

Louis, February 2007

Well done mate you fault find better than some of my qualified colleagues....
The problem is with the thermistor should read between 15 and 20 k,ohms, If not replace it.. dead easy......in the book.

THE GAS MAN

THE GAS MAN, February 2007