Worcester 24CDi dhw fault

[r1gwh]

just to add , the Pressure at normal is set to 1. and I have reduced the HW and CH teamp dials to 2 - made no differerence - and yes the boiler would appear to be overheating - I banging my head against the wall in time to the boiler

 

[kevplumb]

a thought has just struck me (makes a change from the better half)

is the diverter valve moving through the full stroke

could be stuck mid pos

 

[op]

thanks for the info so far- I have tonight just run the CH Only. its ok for about 15min then the pressure needle jumps up and boiler shuts down Leaving the CH demand light on but nothing else. the previous night I just run the HW and again I get hot water for about 4 mins then the pressure needle jumps and the boiler makes very loud banging sound, with the odd bit of steam venting. when I run the CH and then also demand some HW we are ok for about 30 seconds before the pressure needle jumps and the boiler shuts down making lots of loud noises. and yes sometimes both HW and CH lights flash slowly - hope this makes sense.

have you checked the expansion vessel

 

[Agile]

Thats a pretty astute observation! Problem is why!

Most likely to be a pump problem or blockage in the main HE or common pipework.

I know these boilers are meant to be pretty reliable but I do have to say that I go to more than I would expect with faults.

Tony

 

[r1gwh]

i'm not sure about the diverter valve I've not looked at it in any detail. I assume you can see it move ? . will look tomorrow. someone else suggested the Diaphragm.

reagarding the pump- i've removed the screw in the front and spun it as describe on the front panel. as the overheating problem was happing on both HW and CH I rulled out the pump - please correct me if I'm wrong.

I was wondering if there was a sensor not working which should reduce the burner down to keep the boiler at say 85c. i was thinking that the boiler was running on full burn and as a result over heating resulting in the banging.

not sure the expanansion bit , i assume thats whats banging so i have kept clear of it

geoff

 

[ChrisR]

as the overheating problem was happing on both HW and CH I rulled out the pump - please correct me if I'm wrong.

AS it's on ch and hw , it would point to the pump being sludged up , or running slow. The impeller is like 2 circular plates with a 4mm gap between, which can fill up with goo.
You can undo the pump head at the 4 hex socket screws to have a look. Need to drain boiler first of course!
Also a blockage in the main heat exchanger, or anywhere else common, would impede circulation and make things get hot.
If it is just on HW, points particularly to the HW h/e.

Sludge makes them (boilers!)heat up more quickly than they would when clean, so overheating happens , instead of the boiler being able to control itself properly. Sensors and stats can drift with age, too.

For it to turn on for HW the diverter must be moving fully. If it were leaking to the ch, it would be less likely to overheat.

 

[corgigazza]

Had it before were aav did not let air out and because ch thermistor was fitted below this created an air pocket, then the thermistor not read the temp correct and boils the system.

the best way to see if the dhw heat exchanger is blocked is to feel the inlet and outlet of the dhw h/e on the primary side, if the boiler cycles on/ off and the inlet is red hot, outlet cold then no circulation is taken place ie blockage.

 

[r1gwh]

Thanks for all your help , the problem was the Pump , It was an Intermittent fault. The pump was changed last weekend and the Boiler is thankfully working perfectly. it would appear that as the water got hot the pump would slow down and then eventually stop. The boiler then would over heat etc . Again big thanks for all your help.

 

[Agile]

I had a Grunfos pump that did that, went slow when it got hot!

It took me the best part of a hour to diagnose but I think I did it with the mechanical stethescope in the end.

Whenever I took the head off it was working fine because it had cooled down.

Tony Glazier

 

[ShizzyA]

I have no hot water but central heating is working fine. there is no pilot light when I try using hot water but it's fine for the central heating. when I turn on the hot tap it starts for about a second and then stops .. can anyone tell me what this could be?

 

[ollski]

dhw diaphragm, but best on a new thread