Vaillant ecotec 938 heating resume delay faultby 2 minutes

[shab]

Hi

I have vaillnat 938 ectotec boiler installed.3 months ago  the problem with it is when hot water tap is opened even for 4 seconds and closed the heating doesnt resume after 2 minutes. Vaillant have told me hat this is normal and it takes this time to replenish the actostore even  though i have comfort mode turned off for the hot water. please help me find out if there is a flaw with the boiler or a fault.

thanks

[MikeSharp01]

@Nickfromwales will be along shortly and he knows all about that boiler so with luck you will get an answer. PS Welcome to the forum. .

[Jeremy Harris]

Not sure this is much help, but we have a smaller Vaillant Ecotec Plus 831 and there is always a delay when switching from hot water to heating.  On ours, I've watched what the boiler does, and the sequence goes like this.

 

-  Open a hot tap, even for a few seconds, and the boiler shuts down if actively heating, and starts the process of switching to hot water mode.

 

-  The diverter valve then operates, to switch the boiler into hot water mode and this takes a few seconds for the valve to motor to the new position.

 

-  The boiler then runs through the hot water start up sequence, with the fan starting, the pump starting and when the pump kick is detected the igniter fires and the gas valve is opened.  The boiler then checks that the flame is present and if so modulates the gas valve to provide the set hot water temperature.  This process takes maybe 10 to 20 seconds or so.

 

-  Close the hot tap and the boiler senses the flow reduction in a couple of seconds and shuts down the burner, keeping the fan on to clear the burner chamber for a few seconds.  The diverter valve then rotates back to the heating position and the boiler runs though the heating start cycle.  If the boiler is hot (i.e. if it had been running in heating mode when there was a hot water demand) then it will often go into the anti-short cycle delay, with the pump over-run timer on to cool the primary circuit down a bit.

 

-  At the end of the pump over-run delay if there is still a call for heat from the thermostat the boiler will run through the start sequence, the fan will come on, the pump will come on, the pressure sensor will detect the pump kick and start the ignitor and then open the gas valve.  Once the flame has been detected, the gas valve will be modulated to deliver the set heating flow temperature.

 

 

None of these things happen instantly, and each operation takes a few seconds.  If the boiler has heat-soaked during hot water delivery then there is a very high probability that it will go into over-run mode and there will be a short delay with water circulating through the heating circuit until the burner start up sequence starts.  This is pretty normal behaviour.

 

If you want to check what your boiler is doing there should be a way to look at the first level diagnostic codes on the display.  On ours, pressing the "i" button brings up this display, and with the benefit of the table in the back of the manual you should be able to see what mode the boiler is in, i.e., whether there is a call for heat, whether it is in over-run mode or whether the burner is operating.  The symbols on the display may help too.  Ours displays a flashing radiator symbol when there is a call for heat but the boiler is on the over-run timer, a solid radiator symbol when there is a call for heat and the boiler is not in over-run mode and a flame symbol when the burner is operating.  The first level diagnostic codes just give a bit more detail as to what is going on.

[Nickfromwales]

@shab Hi and welcome.

FYI, I've deleted your other post as it's best to keep the subject separate and in one place, ( or things get messy and difficult to monitor ). 

As it's the heatstore it's a different beast to the combi. I'll check with Vaillant as to what the normal sequence of events are, but if it's the exact same 2 minutes or so EVERY time after domestic hot water ( DHW ) is drawn off, then it'll likely be the normal return to service sequence. 

Legionella purge ( purposely high heating ) of the hot storage tanks iirc is factory programmed to happen at 03:00 or 04:00 hrs so the 70+oC water is less likely to be drawn by the consumer, therefore reducing the risk of scalding. 

I'll update ASAP, but I wouldn't panic about it being a fault TBH unless the times / durations of these events differ each time. 

[Nickfromwales]

Ps @shab. Have you fitted the Vaillant wireless room thermostat / controller, like the 470 ? With that you can time the actistore cycles so it doesn't operate overnight etc.