I've also just proved the backfeed issue with how my valves are wired. With both CH and HW on, both valves will remain open until the last of either the HW or CH is turned off.
 
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I've also just proved the backfeed issue with how my valves are wired. With both CH and HW on, both valves will remain open until the last of either the HW or CH is turned off.
 
If you do not follow what I am saying, draw the S Plan schematic and then try and reason what I write

HW zone being active will maintain CH valve open when that Chanel power has been removed by the programmer :whistle::whistle:

I do follow what you are saying. Cheers
 
The water in the F&E tank shouldnt be hot, I would be looking at that air seperator they block all the time
 
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Just updating this with the fix for my Ideal Classic FF260 in case it helps anyone else.....

I had the issue where my boiler was literally boiling the water in the system, causing it to pump over into my header tank. Radiators were far too hot. This was made much worse recently after fitting Tado Smart TRVs which when closed, provided less radiators to dissipate the excess heat. I'd noticed that the boiler thermostat knob on the front of the boiler didn't seem to do anything, so the water feed temp was not being regulated. It was intermittent but most of the time didn't work at all.

So I figured it was either the Potentiometer, The PCB, the relay, or the thermistor sensor. After considering a new boiler as ours is 23 years old I figured I had nothing to lose by buying a can of contact cleaner and giving it a whirl.

After isolating the power I lowered the control box to get access to the PCB and potentiometer, and removed the boiler case to get access to the thermistor.

I sprayed contact cleaner into the potentiometer whilst turning the knob continuously, also cleaning the connections. This immediately made the operation of the knob much smoother. I removed the connection on the PCB and cleaned the connector and pins. I did the same with the overheat stat connector too.

I removed the screw securing the thermistor sensor in the combustion chamber case, removed the rubber tip, and gave that a clean before re-inserting the tip then the sensor and fastening the scree. I also cleaned the overheat stat.

After putting everything back together and restoring power the boiler fired up. But this time the thermostat knob (potentiometer) functioned perfectly and turned the boiler off when moving the knob anti-clockwise.

4 days later and the boiler is still regulating the water flow temperature according to the boiler thermostat position by turning on and off as required to maintain the selected temperature. No more noise, no more pumping over. Lower gas consumption. This is after 7 years of trying to figure out WTF was going on.
 

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