Another Worcester 240 combi problem

[Woody888]

Hi all,

I have different problem with my system. When the central heating is off and cold, and I make a domestic hot water demand (shower, tap or washing machine), the water starts to heat up, then the boiler makes an awful clunking sound and the pilot goes out. Some sort of safety cut out?. I have to relight to pilot and try again, sometime it will go out 2 or 3 times. If the heating is on and hot water in the radiators the domestic hot water is fine.
I have bled the radiators and the boiler base pressure when it is cold is 0.5 bar.
Also, hot water flow from tap or shower seems quite low, but I don't know what is normal as I only moved into this house recently.
Any ideas anyone?
Cheers,
Woody

 

[ogoshi]

The worcester 240 should have a pressure of 1.5 bar not 0.5.when the pressure drops the boiler will shut down . you will need to top it up.the pressure gauge should have a red finger and a black finger.the red should have been set by the installer to show the correct pressure needed to run the boiler.the black needle will show the actual pressure.watch the black needle when filling.

 

[Woody888]

Thanks Ogoshi, but that's strange, cos the fixed red needle on the gauge is at 0.5 bar and the installation book says it should be charged to 0.5 bar.

Hmmm... (scratching of head)

 

[Velvet]

0.5 bar? odd. That suggests it's actually operating under vacuum, surely, since 1 bar is atmospheric pressure at sea level?

I don't know anything about your boiler, but I know mine is set at 1.5 bar (potterton).

Velvet

 

[ogoshi]

woody take the pressure to 1.5 and run the boiler to see if it works.
all sealed systems have a safety valve fitted in the boiler,this will release the water through the safety valve pipe to outside the house if the pressure is too much .

 

[Woody888]

Sorry for not replying to Velvet and Ogoshi, I been away.

Velvet - The pressure gauge on the boiler is not indicating atmospheric (ambient) pressure. It's reading pressure above ambient. The gauge is calibrated to read zero at ambient. Liken it to letting all the air pressure out of a car tyre - if you then put a pressure gauge on the tyre, it doesn't read 15 psi (ambient), it reads zero. For pressure gauges designed to indicate a system pressure, we are not interested in ambient pressure.

Ogoshi - I cranked up the base pressure to 1 bar when the boiler and heating was cold, and when it heated up it was reading 3 bar and dripping out of the relief outlet. I don't know what type of Worcester 240 you have if it runs with a base pressure of 1.5 bar, but it must be different to mine!

More scratching of head....

 

[Ant]

I don't know if this helps but . . . My Saunier Duval Combi has a cold pressure of 1.5 bar which obviously increases when hot. The only time I had water coming out of the safety outlet was when the internal pressure vessel had failed. Obviously this is not the only time it will vent this way but it may be worth looking into. On my boiler you can check the pressure vessel pressure with a tyre pressure gauge although having rubber fingers is useful! Good Luck

 

[ogoshi]

Hi woody im sorry to bring all this up again but ive managed to get a service/installation guide for the 240 as i was very puzzled about this 0.5 bar pressure.I think ive found were we are both getting each other mixed up.On page 7,sealed systems,section 7.5 it states "the 10 litre expansion vessel is charged to 0.5 bar etc etc".
The expansion vessel pressure is made by the air inside the vessell.
We want to increase the pressure in the system by topping up with water.If you go to page 17,commissioning,"set the system pressure"you will see what i meant about pressurising to 1.5 bar.
I hope this helps,as it was very confusing for both of us.
good luck.