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Plumberpro
Plumberpro, Plumber
Category: Plumbing
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Experience:  Heating and plumbing answers. 20 years experience
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I have a riva compact HEM96.24SM/C2 that is failing to fire,

Customer Question

Hi I have a riva compact HEM96.24SM/C2 that is failing to fire, its about three years old.
Called out the local plumber who looked at it for a while and said we need a new one for £2K ............. It had only been serviced satisfactorily in October last year.
Well I'm an electrician so decided to check it out. The error condition (LED's) indicate that the Air pressure switch is faulty but I have checked it and it works fine.
I have checked the flow chart (riva service manual) and in the ignition sequence the fan is not coming on. The fan is healthy (correct resistance and free moving) but on checking the feed to it (meter) it does not get fed with any power at any point in the cycle.
Interestingly if I "fool" the PCB by blowing in the air pressure switch at the right point in the ignition sequence (to make it believe the fan is operating) the boiler will complete its firing cycle and ignite. Of course I did not allow it to fire for more than a second or two without the fan.
I have checked every sensor and micro-switch (continuity and sensor resistance) all are working correctly.
Once that was done I sourced a new (not refurbished) PCB and fitted it but same result, the fan was never switched on.
Is it possible I have two faulty PCB's ? Every sensor and micro-switch is working correctly so not sure what to try next.
Please can anyone advise ?
Peter
Submitted: 7 months ago.
Category: Plumbing
Expert:  Plumberpro replied 7 months ago.
Hi , I would see if the air pressure switch is faulty. The boiler may route through the no( normally open) lead first before running the fan . If the pcb isn't receiving that it may not go on to the next sequence . For the cost it may be worth trying or just check you have no Continuity through it with no call for hot water/heat.I'm sure the pressure has been checked that its above 1.2Also if the temperature thermistors are faulty this sometimes produces some weird results.
Expert:  Plumberpro replied 7 months ago.
Also check the pump is running as the fan won't power u til the pumps running has been proved

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