Vaillant Ecotec plus 428 overactive. Keeps running in S7 and S8 mode.

[John.g]

Thanks. I'm not sure what the 24v link is I'm afraid. There is a wee junction box floating around underneath the boiler. Is that it?

I was not standing next to them while they were working but I did notice at some stage they had opened up the pump in order to remove air. That led to some water spillage.

Just now I switched on the hot water at the timer. This appeared to make the boiler more reluctant to fire which I did not expect. The boiler now seemed to be shedding heat through the pipe to the hot water tank but with the boiler off.

CH man said he would replace the automatic air valve on top of the boiler tomorrow, and generally do some diagnostic pondering. I can see his point in that, as they did not do anything other than replace radiatiors, and then struggle with air, some trapped air may be gumming up the works. Why that would make the boiler get stuck in this S7 - S8 - S7 loop, and keep the water hot in the bypass loop I even though heat is not asked for I find mysterious.

S.07 is the pump overrun time, default setting (D.01) 5 mins. S.08 is Temporary shutdown after heating procedure. Not sure if this is the anti cycle time (D.02), default setting 20 mins but the actual anti cycle time then depends on the heating target temperature, if the target temperature is 70C then the anti cycling time is 2.5 minutes with the 20 min default setting.
Reasons for above?: normal behaviour after heating or DHW period. If the boiler reaches its target temperature +5C for whatever reason, boiler minimum output > heating demand, or, perhaps in this case, mot.valves shut but boiler firing due to faulty end switch, or maybe this 24V link left in.
Apart from the above problem I hope the engineers havn't changed the pump settings causing this pump over into the (feed and expansion) tank as these systems can be very sensitive to the pump settings.

Hopefully, tomorrow will bring some answers.

 

[paleo12]

S.07 is the pump overrun time, default setting (D.01) 5 mins. S.08 is Temporary shutdown after heating procedure. Not sure if this is the anti cycle time (D.02), default setting 20 mins but the actual anti cycle time then depends on the heating target temperature, if the target temperature is 70C then the anti cycling time is 2.5 minutes with the 20 min default setting.
Reasons for above?: normal behaviour after heating or DHW period. If the boiler reaches its target temperature +5C for whatever reason, boiler minimum output > heating demand, or, perhaps in this case, mot.valves shut but boiler firing due to faulty end switch, or maybe this 24V link left in.
Apart from the above problem I hope the engineers havn't changed the pump settings causing this pump over into the (feed and expansion) tank as these systems can be very sensitive to the pump settings.

Hopefully, tomorrow will bring some answers.

Thanks. The problem has evolved in that now, when I switch the hot water off at the timer, the boiler accepts this after a while and produces an S30 status. The pump then switches off. As far as I can see, that is what it should do.

As long as the hot water is not switched off, the pump will keep on running regardless of whether the boiler fires or not. The boiler will occasionally fire up in very short bursts lasting maybe 10 or 20 seconds. In my ignorance of the ways of boilers, I would have thought that firing until the hot water tank had reached the temperature set by its thermostat, and then calling it a day until the tank thermostat calls for heat would be logical.

I'll ask the CH man to check if the tank thermostat actually closes the HW valve underneath the boiler.

 

[John.g]

Vaillant boilers fires up at a high firing rate of approx 65%, they remain at this rate for up to 60 secs and then modulate down to the required firing rate, if the target flow temperature reaches SP+5C then the boiler will start cycling, the circ pump will IMO continue to run, when the anti cycling time has elapsed the boiler will fire up again. It looks possibly like air still in the system, can you fire up the boiler with both CH & HW requested, if it does remain firing, after a few minutes shut off CH and see if it remains firing on HW only.

Also ensure that there is water in the Feed & expansion tank.

 

[Odatmi]

Thanks. The problem has evolved in that now, when I switch the hot water off at the timer, the boiler accepts this after a while and produces an S30 status. The pump then switches off. As far as I can see, that is what it should do.

As long as the hot water is not switched off, the pump will keep on running regardless of whether the boiler fires or not. The boiler will occasionally fire up in very short bursts lasting maybe 10 or 20 seconds. In my ignorance of the ways of boilers, I would have thought that firing until the hot water tank had reached the temperature set by its thermostat, and then calling it a day until the tank thermostat calls for heat would be logical.

I'll ask the CH man to check if the tank thermostat actually closes the HW valve underneath the boiler.

Did you manage to resolve what it was?