Potterton Profile Prima Air Pressure sensing

[mahogany]

A known fault with this boiler is to do with Air Pressure Sensing, either the switch itself, the associated flexible tubes, the restrictor, the venturi on the flue or the boiler cover sealing.

Quite a lot to diagnose, never mind the otehr stuff - valves, sensing, electronics etc.

As a general point, it would be helpful if the start sequence timing was known so we could put more meaningful posts on here when we get probs?

As I understand it, the sequence goes something like this
Check APS contacts are open
Start Fan - wait for normal speed
Check APS contacts close
Open pilot injector
Open pilot gas valve
Sense pilot flame
Open main gas valve
etc etc

Seems to me that as the boiler ages, fans may slow down due worn bearings, flues may get partially obstructed, air tubes and venturi may get partially gunged up (especially the pressure tube as it is inhaling flue gases?) That's why we have the boiler serviced right?

But there must be timing tolerances in the contol electroncis which make some allowances for these various components to age. If the tolerances were too tight, boilers would be locking out prematurely. If they were too slack, they could be dangerous.

Hence my comment about the timings for each part of the sequence. Any comments?

 

[gaswizzard]

What info are you seeking.

 

[gaswizzard]

Open pilot injector

 

[twgas]

there is no electronic lock-out on this boiler - timing is not a factor - if it took the fan 20mins to build up speed the boiler would still light (assuming everything else is OK).
What is the point of your post?

 

[geoff@cetltd]

A known fault with this boiler is to do with Air Pressure Sensing, probs?

As I understand it, the sequence goes something like this

The sequence goes like ths:

If the two white stat wires see a short circuit and tre air pressure switch has a good low ohmic ( ~<1ohm), between the normally closed contacts and common, when mains is applied across live and neutral of the pcb, the fan comes on. The fan activates the APS and when the APS microswitch presents a short circuit between common and normally open to the pcb, a) the pilot solenoid is energised and b) the spark circuit is activated. The spark ignites the gas from the pilot and is sensed down the HT lead by the pcb which then goes on to open the main gas valve solenoid

The "air pressure switch " problem which you quoted is usually a problem with the pcb

 

[mahogany]

Gas Wizzard - sorry I didn't express my self clearly. I just want to understand the steps the control electronics go through for start up and the timings.

Raden's comments are very helpful.

Do these boilers take longer to start from cold? Last week the air being sucked onto the casing was -15 which presumably affects the time taken for the flame to be sensed ?