New supply pipe fitted. Now combi isn't firing up

[thompster]

Hi,
Since changing main lead supply pipe for 25mm MDPE my combi boiler doesn't fire up as it should. I now have to turn the kitchen tap on fully before the boiler fires and have one basin tap (10mm braided hoses) that doesn't get any hot water at all. Previously even a trickle of water would be enough for the boiler to fire up.

The boiler is a Worcester Bosch 24cdi.

I've looked through the commisioning section of the manual but can't find pressure switch adjustment or anything simillar. Is this a symptom of a knackered switch or does something just need adjusting to lower the threshold at which heating starts?

Cheers,
T.

 

[bengasman]

Hi,
Since changing main lead supply pipe for 25mm MDPE my combi boiler doesn't fire up as it should. I now have to turn the kitchen tap on fully before the boiler fires and have one basin tap (10mm braided hoses) that doesn't get any hot water at all....

Could it be that you have done something wrong with the waterpipe?

 

[thompster]

Nope, since apart from anything else I didn't lay the MDPE.

Supply pipes prerrty much either work or don't work. If water comes out of the end at a pressure/flow rate commensurate with the size of pipe it's working. None of the plumbing in the house has changed and it worked before increasing flow rate and didn't after.

I'm guessing it is to do with the relative pressures either side of the pressure switch, but could possibly be because now the pressure with a tap turned half-on is higher than the static pressure was before with the tap turned off.

 

[namsag]

Coincidence your diaphragm in divertor valve is going and will shortly fail completly

 

[thompster]

Thanks Namsag.. found a load of stuff on that now and sounds like the problem. Presumably the Diaphram was just about coping with low pressure but not with the higher pressure now.

That will give me somthing to do next weekend..

cheers,
T.

 

[namsag]

Have fun
guys know what i mean

 

[roguetrader]

good luck!

 

[mickyg]

this is not a good first job for diy boiler work. I'd seriously recommend getting WB on a fixed price repair. Don't phone me, the phone will go dead when you tell me the job

 

[thompster]

So, despite the warnings about this being a really difficult job I went ahead and bought a new diapraghm and fitted it this morning. I have to say it wasn't difficult at all. Getting some of the retaining clips back in during reassembly is a bit fiddly but thats about it. All in, it took just under 2 hours including reading the service manual.

If anyone is thinking about trying this I'd say as long as you are mechanically minded and have the service manual then go ahead. The job involves removing the filling loop (5 mins) Removing the heat exchanger (5 mins) and removing the diverter valve itself. That took me the best part of an hour as it took a lot of wiggling before it pulled away from the outlet pipe on the back. Once apart you clean up the valve and filter, and replace the diapraghm using the instructions supplied with it. Reassembly is the reverse, not forgetting to replacing every o-ring you come to. After testing, I had one drip from the pack of the heat exchanger (knew I should have used boss white on it). Nipping up the joint a quarter turn fixed that.

So - thanks to the poster who told me what the problem was...and for the rest of you, if you want a REALLY difficult job, come over to mine and balance the carbs on my vfr400. I've started that job twice and given up both times...

Cheers,
T.