Intermittent fault on combi boiler

[ivanrebello]

Please help.

I have a Ferroli combi boiler model Optima 801 and have an intermittant fault on the hot water side.

When running the hot water tap or having a shower the hot water regularly goes cold and I have to switch the heating on and leave it for a few minutes before the water gets hot again.

Sometimes during a shower I have to go through this process a number of times.

On this make of boiler when the hot water is operated the heating pump automatically stops and re-starts when the hot water is switched off.

I have checked the manual and understand that the problem may be the hot water sensor. I have replaced the sensor (part no 800310) a number of times (new one now) and recently the problem has got worse.

Understand that if the sensor resistance is low i.e. below 500 Ohms the sensor trips out.

Are there replacement sensors available that provide above 500 ohms when the incoming water temperature is cold or is there an adjustment on the pcb board that can be carried out.

Or am I completely wrong and the problem is elsewhere.

Thanks

 

[picasso]

Are there any fault led,s showing when hot water cuts out?, it could be the flowmeter is faulty.

 

[Agile]

You are completely wrong.

The fault is probably the flow sensor. When it stops try turning on a hot tap AS WELL as the shower and see if that brings it back on.

It could also be the boiler overheating!

Ferolli sensors do seem very unreliable though, usually going open circuit.

Tony

 

[picasso]

who is completly wrong ? ferroli call it a flowmeter or a completly different part a dhw sensor, which one do you mean?

 

[ivanrebello]

Hi all,

With the heating in off position and all hot water taps in the closed position, indicator lights 1 and 4 are on.

When any of the hot water taps are opened only lights 1 and 2 are on.

This indicates that the problem is not the flowmeter but either the sensor or another problem.

Could the new temperature sensor also be faulty?

 

[ivanrebello]

Hi all,

For those suffering from similar problems I would suggest disconnecting all the cables from the PCB and reconnect them again.

It appears that over a period of time the contacts tend to get slightly corroded and therefore the contacts are week. Reconnecting them again makes a firmer contact.

Fingers crossed the problem appears to have disappeared.

 

[DP]

OP little knowledge is a dangerous thing. I am sure you are being helpful when you make that suggestion but I can see plenty reading what you have written and in feet first to start pull PCB wires off the board, in some cases killing it.

In all the years I have been plying my trade, I have come across loose connections but never seen corroded contacts calling for total disconnection. Tags are most often copper, with coating (sometimes silver) so unlikely to corrode unless there PCB has been watered like a plant will.

Proper method of fixing faults is to carry out systematic checks to locate area of defect and then corrective action- might just be, like you say, bad connection.