topping up the pressure in my central heating system

[AMF38]

Hi
I have a Glow Worm BG330 boiler which is coming up with a F5 fault. From what I have gathered so far, I understand this more than likely has something to do with low pressure. However having searched the loft and piping within the cupboards I cannot locate a filling point and associated pressure gauge to top up the system. The basic control panel on the boiler does show the pressure for a split second when first switched on, before changing over to show the temperature.
Is there another way to top up the pressure with this type of boiler and system, and if so how?

 

[DIYDANDY]

F5 is (I think) not a low pressure problem. Do you have the owner manual?

Have you done any work on he system?

 

[AMF38]

No work has been carried out. The system has been running for short periods over the last few months, and then recently for longer. Everything was fine two days ago. I did bleed the radiators as one felt cooler in areas but got very little air out.

According to the manual the F5 fault relates to;
Overheat stat operated
Maximum temperature exceeded
Check thermistor connections
Air in system with thermistor at maximum setting
Faulty overheat stat connection
Check that pump is wired into appliance and not from programmer. This would cause no pump overrun.

Any ideas?

 

[DIYDANDY]

This might help

http://www.howtomendit.com/answers.php?id=96669

 

[AMF38]

Thanks, the link it confirmed what I'd found in the manual moments earlier, and the reset got the boiler back on line. What would cause it to trip though?

Now, however I am left with another issue. After hours of tinkering it appears that the CH and rads work when the HW is timed to come on, and I believe vice versa.
As no major work has been carried out, would I be correct in thinking this comes down to the 'mid position actuator'? The model is the BGMVSP23.
The pump seems to kick in when I manual move the black lever on top of the actuator, although this is not always possible. When switched off completely the black lever rises to the top and is loose. I can hear the motor and cogs turning when I manually move the lever. I have also noticed that the unit feels very hot on some occasions, and the lever cannot be moved. Could this be because the lever gets stuck and the motor is trying to turn the valve?
Or could it be that the three way valve is jammed or broken? We still have hot water but the heating comes on in line with the hot water timings and not when I put the CH on permanently with thermostat set high???
Any ideas?