Worcserter 24CDi DHW issue

What flow rate does DHW turn on? My boiler works fine for CH but I have noticed recently that DHW has been problematic. The HW sometimes does not turn on until the tap is turned fully on and when I back off the flow rate to get hotter water, it turns off again. Usually I can get it so that is just over hand hot and occasionally it does get hotter than usual at much reduced flow rate. Today I could not get HW in the bathroom and I left the tap running full on and checked the boiler and it was not calling for heat. I used a 2l jug and stopwatch and the max flowrate is about 5 l/m for the bathroom and the kitchen about 12 l/m. I am guessing that it is something wrong with the diverter valve microswitch but wanted to check.

I do have a service contract for the boiler but I wanted to check before I get told that I need a new boiler since the boiler is over 20 years old.

 

Most likely that the DHW diaphragm is split, or perished and needs replacing

 

Thanks Ian,
Once I clear a space in my garage I will call in the engineer.

 

Everyone in the trade hates doing a CDi diverter, many actively avoid it...there's every chance you'll be fobbed off as an uneconomical repair.
In reality it's a straightforward job.

 

Thanks Gasguru, good to know.

 

Easy job, glue 5p onto the plunger . Job done.

Joking. Who's your service contract with. Make sure you tell them to check the micro switch when they're diagnosing as above they'll probably try fobbing you off.

I quite enjoy doing them, as long as I have the time

 

Contract is with Domestic and General but it is Worcester engineers who have done any work in the past and I found them very good. Last year, it was the first service visit for several years and the guy gave me a new bracket for the balance flue because the perforated metal strip was no longer allowed.

 

there is noting hard about servicing the valve, just that poke and go merchants havent a clue how to, personally I would service them all day long and I hate Worcesters

 

I don't service them but I have been happy with it for over 20 years. The heat exchanger sprung a leak which cause the PRV to need replacing. The Expansion vessel also needed recharged once. I had an interesting issue where the radiator temperature dropped. I the dead of winter, I like to run the water temp at max which should be 84C but sometimes it would drop to about 65C. Twiddling the temp control would reset it. I built a unit to monitor the boiler flow and return temperature and log the on a computer. the resultant graphs were very interesting. It took the boiler about 20 minutes to reach the point where the gas valve started to modulate. Then as the return temp got within about 7 degrees of the flow, the burner shut down and restart 5 minutes later. I could show the Worcester engineer the graphs when the boiler was not producing the maximum heat. He just shook his head and replace the main board. He couldn't believe the amount of work it put into proving the fault. Probably just a dodgy heat control potentiometer. The boiler has worked fine until now.

 

The expansion vessel should be checked every year...few will last more than a couple of years before going flat. What saves most system from over pressure is trapped air in the rads..

 

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