HW/CH Problem with Worcester Bosch 240

[Monchan]

Hi. I've just moved into a new property which has the above combi bolier. Have had a couple of problems over the past week:
1. When CH is ON HW runs fine but it's summer so don't want CH on
2. When CH is OFF HW seems to work fine but eventually the overheat thermostat kicks in - seems the system is getting too hot. I have to keep resetting the overheat switch.

3. When CH is ON the radiators get piping hot irrespective of setting (and a couple rattle)

I've read a few threads and it seems it might be the Diverter valve/diaphragm. Not an expert so will probably call an engineer out...any other advice? What is likely cost to be?

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please see forum rule 9

 

[Agile]

As long as the HW turns on the boiler at about 3 li/min then the diverter is probably ok.

I would normally suggest you measure the temperature sensor resistance.

However you seem to imply that the boiler gets too hot on both HW and CH so that would point me towards a gas valve setting problem ( which is a CORGI job ).

Tony Glazier

 

[ChrisR]

Symptoms not quite clear but possibly a sticking microswitch on the end of the diverter valve - there are two. Often due to a water leak. If it thinks the tap's running when it isn't the boiler fires... heat gets to the overheat stat before it gets to the HW sensor because the pump isn't running(?)... boiler cuts off.

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Edit - hadn't seen Tony's post. There we go in totally different directions, one/both of us possibly misunderstanding/missing something. SHows something about diagnosis from a keyboard!

Have a look at the end of the diverter valve where the black plastic switch box attaches to it (it swivels) if you can see evidence of a leak it would be telling.
DV is brass thing on the left with switch box towards you.

 

[Monchan]

Hi again. Thanks for the replies. Apologies if my explanation of the problem is a little confusing.....Like I said, with CH ON HW is fine. With CH set to OFF the system works fine until the FLOW and RETURN pipes get incredibly hot and at some point the overheat thermostat must trip, cutting off HW completely.

I have BG coming for a gas supply check in a couple of days, and might ask them if there's an issue.

 

[ChrisR]

Always room for fog...

Turn ch off
Does the boiler come on? It shouldn't.

Then Turn HW tap on. Does it overheat while you're running water or after you've turned tap off?

When you say "when ch is on..."
Turn CH on at boiler but off at wall thermostat - assuming you have one.
Do the rads get hot?

Do have a look where I said - couple of screws hold the front lower panel up I think.