Baxi 105HE Combi cutting out ~ daily, 60deg fault light

[anthonyl123]

About every 12 - 24hrs the boiler cuts out. Leave it for about 20mins and then turn knob to off and back to CH and fires up. Try too soon and it doesn't work.

Diverter valve was replaced a couple of months ago but this fault started beginning of November. Some enquiries have pointed at the top pin not fully retracting though it clears the microswitch after 2 or 3 minutes. Pin is free moving and diaphragm all clear so don't understand why it doesn't retract. The DHW pin retracts immediately. Is this a red herring or some other underlying fault?

Otherwise for 10hrs or so the boiler works as expected, on/off as temperature is reached, hot water when needed. Pressure from 1.0bar cold to ~2.0bar when up to 60deg.

If I turn selector switch to Off and then On at other times the chances are the fault condition will display and I have to wait the 20mins before it'll kick in.

 

[SavageW]

Should make the micro switch almost instantly as the pump kicks in mate,Iv had it where diaphragm looks clear but could be hairline split in it.Also you’ve got the small sensing pipe that comes from the bypass into the valve could be partially blocked/restricted
*just re read,do you mean the pin doesn’t retract after demands ended for couple minutes if so that would be cause the pump will over run for that time

 

[anthonyl123]

Just to be clear - the pin rises as soon as the system is switched on and activates the microswitch (at least as best as I can tell). If I turn the selector to say DHW only (with no draw of water) then the pin lowers after a few minutes. Hard to tell if it is clear or not of the microswitch and it doesn't in any event fully retract. The other pin for the DHW does fully retract.

I'm not sure what is meant by "pump over-run". I thought the pump would keep pumping for a few minutes regardless and then come to a stop. It's hard to tell if the pump is pumping or whether something else is transmitting sound through the system (fans).

As far as I know the diaphragm and sensing pipes are all clear but obviously can't rule anything out until the problem is cured but I don't understand why it is operating normally and as expected for most of the time then chooses to stop.

 

[SavageW]

Yeh pump over-run if you had system on then turned to dhw only the pump would carry on running for few minutes meaning the spindle wouldn’t retract for couple minutes if not only a bit an not fully.Could be iron oxide/sludge on pin

 

[anthonyl123]

Thanks. Pin, diaphragm, venturi hole etc were checked yesterday. This is a 2 month old diverter valve.

If I go now to the boiler (its been running happily on low all day) and turn the selector to Off then On again the fault light will come on and I'll have to wait 20-30mins before turning Off then On again to fire up.

 

[SavageW]

Be looking down lines of the micro switch then could be that it’s getting stuck after demand an not unswitching once the spindle has retracted

 

[anthonyl123]

Makes sense, I'll see if I can detect if it's moving enough but what I don't get is if the timer is set for 24/7 and on low why should the pin need to retract at all and deactivate the micro-switch. Is there logic to say the pump has to have a break every 12 hours or so?

 

[SavageW]

It’s just a pump proving switch really,if your ch is set on constant at timer it will still eventually shut off once then room thermostat has reached temp or the boiler stat.Its never going to run constantly

 

[SavageW]

Are you working on this yourself by the way or have a Gas Safe guy

 

[anthonyl123]

I'm trying things, like switch on/off, set timers, look at the pin, myself. A Gas Safe guy had a look at the diverter diaphragm etc but left scratching his head. I'm the one whose wife says it's cold at 5am and have to go and reset the boiler in the back utility room and am constantly thinking about the problem. I'm stuck with the logic of why it goes 12+ hours quite happily and then fails quite consistently.

If the pump has to stop during a 24hr cycle then the microswitch theory makes sense because that would behave the same as my turning the boiler off then on, both resulting in a fault. Otherwise what else can be happening?