Vaillant boiler change in operation

[Dunbar]

My Vaillant boiler now only fires up for around 30 secs then goes off. The egg timer symbol then appears and flashes for several minutes. After that it fires up again and heats the rads. Would be grateful if anyone could suggest why this is happening. Thanks.

 

[Brambles]

The boiler is cycling. Ie. Cutting in and out too frequently. The egg timer is in effect blocking the boiler from firing, until the anticycling time limit has passed.

 

[Dunbar]

The boiler is cycling. Ie. Cutting in and out too frequently. The egg timer is in effect blocking the boiler from firing, until the anticycling time limit has passed.

Thanks for the feedback.

 

[Dunbar]

Thanks for the feedback.

I was just wondering why the boiler is suddenly recycling after being on for such a short period.

 

[John.g]

Is this happening at its first startup say in the morning or is it after a zone shuts or TRVs start closing in with boiler on for some time?
Its probably exceeding its target temperature by 5C and going into recycle, what is the target temperature set to?.
What model Vaillant?.

 

[Dunbar]

Is this happening at its first startup say in the morning or is it after a zone shuts or TRVs start closing in with boiler on for some time?
Its probably exceeding its target temperature by 5C and going into recycle, what is the target temperature set to?.
What model Vaillant?.

Happens every time the boiler fires up, when room temp drops below desired temperature. Flow temp set at 75 degs. Only happens the once, and then boiler operates normally after a few minutes until desired temp reached. Boiler is Vaillant ecoTEC plus 418.

 

[John.g]

Have you got a manual or/and a automatic (ABV) bypass valve, if a ABV check its setting index, the system temperature may still be too high after the last shut down to allow it not to reach 80C and burner trip on the initial fire up, if you have a 3 port valve then bypass not required.
Can you see what (d.01) the pump overrun time is and (d.02) the anticycle time likewise.
Can you also check the flow/return (d.40/d.41) temps next time its firing and also the circ pump make/model/mode&setting.

Your name rang a bell there so I looked back through your thread on the last? problem with this boiler, you said the engineer changed a sensor then, do you know what sensor he changed?.

 

[Dunbar]

Happens every time the boiler fires up, when room temp drops below desired temperature. Flow temp set at 75 degs. Only happens the once, and then boiler operates normally after a few minutes until desired temp reached. Boiler is Vaillant ecoTEC plus 418.

Bit more info. If I bring boiler on by turning room stat up, boiler comes on until it reaches 75 degs. If I wait until room temp falls below room stat setting, boiler comes on only for 30 secs by which time it has only reached around 35 degs and then goes off and egg timer symbol flashes for a few minutes before boiler comes on again until it reaches 75 degs.

 

[John.g]

What is the make/modelof the roomstat?.
Can you also have a look at post #7.

 

[Dunbar]

What is the make/modelof the roomstat?.
Can you also have a look at post #7.

Stat is Honeywell T4360. Need a bit of time to try and work out answers to questions in post 7. Thanks for info so far.

 

[Dunbar]

Stat is Honeywell T4360. Need a bit of time to try and work out answers to questions in post 7. Thanks for info so far.

Not sure if relevant and/or whether it might point to the room stat as issue, but boiler fires up and stays on until temp reached for hot water.

 

[Basher]

Not sure if relevant and/or whether it might point to the room stat as issue, but boiler fires up and stays on until temp reached for hot water.

That Honeywell stat has a number of versions/options (I think there's a letter at the end of the serial number indicating which), and one version has a "heat anticipator" the exact operation of which I don't understand. It might be the little resistor (heater) found in some thermostats to reduce the hysteresis of the sensor. Could that be contributing to the issue - it shouldn't I guess?

 

[John.g]

Yes, that's how the anticipator works, if the stat is knocking off the boiler then the pump will run for the d.1 the overrun set time if it's going into anticycle then the anticycle time is set in d.2 there is also a s parameter telling you if its overrun or anticycle. The remaining anticycle time will also be displayed in one of the d parameters I think, if boiler is in recycle, remaining anticycle time is shown in d.67.
d.1 overrun defaults to 5 minutes, the anticycle actual time is per table, below, if thehe target temp is 75C then the annticycle time is 1 min irrespective of the set time which has a default setting of 20, apart from setting 1 (min) which strangley enough gives a actual anticycle time of 2 minutes.

 

[Dunbar]

Thanks for all replies. I thought I was out of warranty, but on checking, I have till March. Called Vaillant engineer out, who fitted new pcb and flow and return sensors which appears to have fixed early recycling issue.