Worcester Bosch 24CDi - overheat cutoff

[Donkadocus]

I have just moved into a new flat. The heating and hot water appeared to be working correctly when I moved in. I thought is would be a good idea to bleed the air out of the radiators, sigh…

I am using the user manual located at http://www.worcester-bosch.co.uk/cache/file/186/user-manual-for-cdi--discontinued-05-07.pdf as my only point of reference.
When I moved in the pressure gauge read 0 which I assume means I have an ‘open vented heating system’? How can I confirm this?

SYSTEM PRESSURE GAUGE
The red needle has been set to show the sealed system pressure which is required for the appliance to operate effectively. The grey needle will show the actual pressure in the system. This does not apply to any open vent system.

The boiler is indicating ‘overheat cutoff’ as described below:

Central heating and domestic hot water demand indicators: BOTH FLASHING SLOW : Overheat cut-off (once per second).

I reset the system by pressing the ‘Reset Button’ for five seconds and then follow these instructions:

TO LIGHT THE APPLIANCE
Check that the water valves to the central heating circuit are open. On sealed systems check that the grey needle on the pressure gauge is not below the required pressure. Switch on the mains electricity. The green power on indicator will light. Set the room thermostat, if fitted, to maximum. Turn the central heating temperature control knob to ‘MAX’. The red central heating demand indicator will light. The burner will light and the red flame detection indicator will light. Set the central heating and hot water temperature control knobs and the room thermostat, if fitted, to the desired temperature.

I have no idea how to ‘check that the water valves to the central heating circuit are open’ but I have not touched anything since I moved in.
As stated I ‘think’ my system is not sealed.
The ‘green power on indicator’ lights as expected.
The ‘red central heating demand indicator’ lights as expected.
I don’t know what ‘The burner will light’ means?
The ‘red flame detection indicator’ does not light, which is not expected as it should.

There is no heating. If I run the hot tap the ‘DHW demand Central heating indicator’ lights but there is no hot water. The ‘red flame detection indicator’ still does not light.

After a while the system appears to overheat and indicates ‘overheat cutoff’.

Any help would be gratefully received. If it is not obvious I am a complete novice so please be gentle.

 

[lifesagasman]

first things first use your manual to raise the pressure in the system to around 1 bar. you'll need use a special key in the 'filling loop' under the boiler to do this. then reset and see if boiler responds to hot water demand. (turn on hot tap)

 

[Donkadocus]

first things first use your manual to raise the pressure in the system to around 1 bar. you'll need use a special key in the 'filling loop' under the boiler to do this. then reset and see if boiler responds to hot water demand. (turn on hot tap)

I have ordered the required key from ebay.

How do I know that I have a sealed system and not an open vent one?

 

[nickso]

on a cdi the vent pipe comes out of the top left of the boiler if its open vent.

 

[Donkadocus]

on a cdi the vent pipe comes out of the top left of the boiler if its open vent.

There is some sort of airhole that shoots a bit of air out of the top left of the boiler when it gets switched on. Is that it?

If so, then I assume I can't raise the pressure and I need to try something else?

 

[nickso]

no thats the auto air vent.

i would assume you have a sealed system. you need to find the key and refill it.

 

[Donkadocus]

So I have the key.

Question 1: Are you supposed to refill the boiler when it is on or off, or doesn't it matter?

Re-pressurising The System
Insert the bayonet end of the filling key into the corresponding cut outs in the filling loop housing and twist to lock the key in place. Turn the grey knob anti-clockwise to allow water ingress and fill until the required pressure is reached. Turn the grey knob clockwise to stop filling and remove the filling key by lining up the bayonet end of the key with the cut outs in the filling loop housing and withdrawing the key.

Question 2: It seems that my boiler doesn't have the 'grey knob' referred to in the manual. Instead there is a white plastic thread that I assume means the knob is missing.

Is this the correct replacement knob?

http://www.boilersparesuk.co.uk/proddetail.asp?prod=78980

Thanks

 

[pappyon]

I can't for the life of me think why anybody would remove the filling knob. It is a small grey hexagonal plastic knob just to the right of where you insert the filler key.

The link you point to does not show any knob of any kind. There is nothing there so I can't comment on whether that is it or not!

I have one of these boilers in a flat I moved out of and topped it up just this morning.

Put some saliva or a very light rub of vasenlie on the o rings on the filler key before you insert it. It makes it easier to insert and ensures the o rings don't get damaged! Twist the key to lock it after you have inserted it fully.

Do it when the system is cold and switched off and take it up no higher than 1.5psi. Don't overtighten the grey know when you shut it off, it is quite delicate!

Remember to remove the key when you are finished. It's something to do with the building regulations

 

[nickso]

grey knob has broken. use a pair of pliers instead.

 

[pappyon]

"Do it when the system is cold and switched off and take it up no higher than 1.5psi. Don't overtighten the grey knob when you shut it off, it is quite delicate!"

Excuse my mistake. when I quoted PSI I actually meant 1.5bar
Not much difference eh?

 

[Donkadocus]

Tried everything - nothing happens basically.

With filler key in place - turned using pliers, nothing happens
With filler key not in place - turned using pliers, nothing happens

What now please?

 

[nickso]

get someone to fit a new filler if its not working. easy job.