Worcester Bosch 24 cdi combi. pump questions.

[ukdan]

Hi
I have yet another problem with my combi. When the dhw is being used, after a little while the flame will go out for a few seconds and then come back on. The pump is seemingly running fine but it gets too hot to touch. I've taken the vent plug out the centre of the pump and water pours out through the hole, even with the pump off. The pump spins fine and the water, which is clean, still pours out. Each time i take the vent plug out, there is a release of pressure, even if i put it back in and take it out straight away. Am i right in assuming that the pump is knackered and just needs replacing? Also, just out of curiosity, why does the pump need to operate when only the dhw is being used?
Many, many thanks for any advice.
Cheers
Neill

 

[Andygasman2010]

Forget about the pump it's fine. Sounds like you have a blocked plate heat exchanger.

The pump runs to circulate hot water around the main heat exchanger and plate heat exchanger.

Look at the flame. Just before it cuts out does it go to low flame, or from high flame straight to off?

 

[ukdan]

Thanks for your reply, Andy.
I've just been watching the flame while the shower was running. After aboout 2 minutes the flame just went straight out. A few seconds later it sounded like the pump switched off and came back on almost straight away. The flame went out twice during the shower. the pressure gauge "blips" at the same time as the flame going out too.
When you say a blocked plate heat exchanger, do you mean the one behind the drop-down control panel? If so, is it easy to unblock? I've taken it off a few years ago when i changed my diverter valve so i've got an idea how to remove it, if its the one you mean.
Thanks again for your help
Neill

 

[Andygasman2010]

It's most likely that your plate heat ex is blocked, it's the one you describe. When you remove it you'll probs see black flakes come out of one side of it, tap it lightly while running water through it. maybe soak it in X800 or something. You could even take it to the garage and jet wash it!

Some of the other guys might have some better tips on cleaning it out

 

[Alfredo]

You can think its clear and there is still loads of crud/flakes inside the thing. I have found a rubber mallet useful for tapping the heat exchanger, hard but not too hard, and it dislodges loads of stuff when you flush it through with cold water. Sometimes it takes a long time before you get most of it out..you'l never get it all. Expect to be tapping and getting stuff out for an hour, it just gets less as you go on. I've had good results doing this and its a lot cheaper than a new heat exchanger.

Don't be tempted to use washing up liquid to help the flush....don't ask me how I know.

Alf

 

[ukdan]

Thanks for the help, guys. I've just got to get an 'o' ring set and i'll be away. Would soaking the exchanger in a weak bleach solution help or would that not be advisable? Hopefully i can get it sorted as it's starting to give me ear ache. She doesn't like it when the shower goes cold.
Thanks again for your advice. It's much appreciated.
I'll let you know how i get on.
Cheers
Neill

 

[ukdan]

Morning, fellas.
Well, i went and spent £13 on an 'o' ring set and got stuck in. I took the heat exchanger off and gave it a thorough jet washing in every hole i could see for about five minutes. Put it all back together and the problem is still there. Any ideas where i can look next?
Cheers
Neill

 

[Andygasman2010]

The fault you describe sounds typical of a blocked plate heat exchanger, it may still be blocked. Did you use any cleansing chemicals to do it?

 

[bazdaman]

it takes time and chemicals to clean one properly. try again

 

[ukdan]

I haven't used any cleaning stuff on it. I'm just taking it all apart again. I'll pour some strong white vinegar/water into it and give it a good shake then leave it to soak for a few hours. Thanks for your help again. Hopefully i can sort it this time.
Cheers
Neill

 

[ukdan]

So. I've left the HE soaking in some de-scaler for a while then jet-washed it out. Put everything back together and tried it. Now the bloody thing sparks till the flame comes on then stops sparking. After a second or two it starts sparking again. Then it's flame out, lock out. No hot water. No heating. I can't see where i might have done something wrong.
Any ideas, fellas?

 

[nickso]

no water in the pcb housing? classic error on one of these.

 

[ukdan]

i had it covered with a towel whenever water was going to go near it. It seems dry enough.

 

[ukdan]

By using the art of witchcraft i have managed to get the flame to stay on. However, after spending the best part of the day on my knees, i still have the original problem. Think i'll give up for now. Until i can be bothered to take it all apart and stuff some more de-scaler down the heat exchanger.
Thanks for your time, fellas.
Neill

 

[kevsuths]

The other thing to check is the pump manifold. The outlet connection can block up and cause the problem of it overheating. It is worth checking this if you have cleaned out the DHW heat exchanger.