plumbing ravenheat combi boilers

[terrycuttlefish]

I have a problem with a ravenheat combi boiler,no manul and i can not get to the badge.The central heating is fine,the hot warter down stairs is good but the upstairs hot water runs hot when first turned on then goes cool and then cold.The boiler runs for about 30 to 40sec and then turns off for about 30sec and then turns on this goes on and on untill you turn the upstairs hot tap off.any help would be great,
all the best,
terry

 

[Andygasman2010]

Sounds like either the DHW diaphragm worn. If your unlucky the heat exchanger could be scaled/blocked.

 

[terrycuttlefish]

Sounds like either the DHW diaphragm worn. If your unlucky the heat exchanger could be scaled/blocked.

thanks for that,now is the diaphragm and the diverter value all in that brass body in the centre of the boiler? all the primary and the hot waterpipe(10mm pipe) run into it.
terry

 

[Andygasman2010]

It's a brass round disc shapped thing, held together with about 6 bolts i think... the diaphragm is in there. You just need the cold mains off to change it, heating system can be left full. Even though the mains is off there'll still be water in there so make sure the boiler is electrically isolated and put a dish under or something

 

[terrycuttlefish]

thanks for that alert .can you tell me whey the hot water is okay down stairs but not up?

 

[kevindgas]

heating system can be left full.

only if you turn off the isolators on flow/return and reduce the pressure in the boiler

 

[Andygasman2010]

heating system can be left full.

only if you turn off the isolators on flow/return and reduce the pressure in the boiler

Hmm am I missing something? If only changing the DHW diaphragm, why does the heating system need to be touched?

 

[Agile]

Probably because the OP has not specified the boiler model and most diverters on that make have to be removed to replace the diaphragm.

To confirm the fault I would be measuring the minimum DHW flow rate at which the boiler fires up. Should be about 2.5 li/min.

Tony

 

[kevindgas]

Probably because the OP has not specified the boiler model and most diverters on that make have to be removed to replace the diaphragm.

Tony

yep!! in fact very few are positioned so as to facilitate changing the diapragm (a task i never do nowadays) always change the whole thing as had to many that fail to operate correctly after a rubber change!