ideal icos he12 fault

[brosnan]

I have an ideal icos he12 boiler which is attemtping to ignite even when the external controls are not calling for heat.

It attempts to ignite on a continous 3 to 4 minute cycle even though the room stat is at 10 deg C and the programmer is switched off. I have checked the stat and it does function normally. I have substituted the drayton tempus 7 programmer for its modern equivalent and there is no change.

The boiler is not showing a fault code, it is showing c which idicates the boiler is active for central heating. The blue neon light goes from blinking, indicating that no flame is detected, to being lit permanently indicating that the flame is being detected. It continously alternates between the two states.

I had the pcb changed in Dec 2009 from the old black version to the new orange version and up until now it has been fine. Can anyone help please?

 

[Andygasman2010]

What kind of system is it on? Two zone valves or a Y-plan?

Does the boiler get hot when it fires up? If an end switch was stuck on one of the valves it'd fire up but the heat wouldn't be able to go anywhere making the boiler cycle.

If it's not a demand from external controls, it'd only be the PCB

 

[brosnan]

It has a mtotrised valve on the CH side and a separate valve to the cylinder which I think makes it an s plan system. The boiler doesn't get hot because it doesn't fire up (unless the programmer allows and the room stat is up). When the programmer is calling and the stat is teurned right up it functions normally. The end switch is not stuck on the CH valve, I can clearly see it moving over and returning again when the stat is turned down or the prgrammer switched off.

I am suspicious of the pcb as this has been changed once before, however, ideal charged £240 last time and I was happy to pay it for a years guarantee as the cheapest I could buy a pcb for was about £190. I have spoekn to their technical team and they refuse to accept it might be the pcb and suggested it was something else in the system.

 

[Andygasman2010]

It does sound more like a system problem to be honest.

The valve/s would return as normal even if the end switch was stuck so it wouldn't be apparent without doing some checks anyway.

When the boiler is cycling as you describe feel the flow/return pipes as close to the boiler as you can to make sure there's no heat.

Are you able to do any electrical checks yourself?

 

[brosnan]

'Ideal' technical have suggested it is a system problem. I thought that if the motorised CH valve was seen to be returning then it is functioning but if I understand you correctly then this is not the case, it may appear to be working from the outside but stuck on internally. I have felt the flow and return pipes just above the vavle and it felt as though some water was passing through it (the pipes were still hot but this might have just been residual heat). I think my next step is electrical checks to confirm if the valve is stuck internally and still calling. I would guess that I would be measuring the supply voltage to the boiler with the programmer off and the room stat turned down? or something else?

 

[Garfeild]

The valve may be returrning,but the microswitch that switches the boiler/pump may be stuck.

 

[Andygasman2010]

Turn off the clock but leave the power on, make access to the boiler terminal strip (if you have the manual for the boiler there will be a diagram in it) and check power on the switched live. If there is, it's an external fault.

Even better, pull out the PCB and locate the 4 way 3 wire connector plug near the fuse, it's got brown, black, and blue wires in it. Set your meter to VAC and put it accross the blue and black wires. If you have power there you have an external call for heat.

 

[brosnan]

The problem has finally been resolved, at least for the time being. A series of tests with a multimeter identified power on the switched live with the programmer off. The Drayton ZA6 motorised valve has a removable actuator which can be easily removed. By unscrewing the cover the micro switch was exposed. The micro switch could be operated with the end of an electrical screwdriver causing the boiler to fire or switch off. This activity must have unstuck the micro switch as it began to behave normally after this and has not faulted since. I was prepared to buy a new motorised valve but have left it for now. If the fault returns I shall buy one. Incidentally the ZA6 is not so easy to source as a ZA5 which have 28mm and 22mm ports respectively. Drayton technical said that I could substitute the actuator from a ZA5 onto my ZA6, negating the need to drain the system and change the valve, so long as the white wire is not being used which it isn't. I was told that it is rare for the white to be used. Thanks for your help guys.