Any Vaillant boiler experts here?

[PiMike]

My ecoTEC plus 418 was installed in 2009 and I have recently started monitoring the ebus (mainly as a retirement hobby ...). It seems to be behaving strangely and I'd appreciate an educated opinion on this please.

 

When CH demand starts, the boiler fires at 66% (d.0 = 12kW). When Flow Temp Desired is reached (55C) the burner modulates down to 28% (the boiler minimum of 5kW). So far so good, but the flow temperature then immediately starts to rise and when it reaches 57C (exactly) the burner cuts out. 18 minutes later it fires up again and the cycle repeats. Is this normal?

 

Mike

 

[JohnMo]

Seems pretty normal, you are getting plenty of run time.  If you look at the return temp, this is slowly increasing over the burn period.  The flow temp increase is a response to the return temp increasing, the boiler is trying to manage delta T.

[PiMike]

1 hour ago, JohnMo said:

Seems pretty normal, you are getting plenty of run time.  If you look at the return temp, this is slowly increasing over the burn period.  The flow temp increase is a response to the return temp increasing, the boiler is trying to manage delta T.

Ah, I see that now. Thank you John!

 

Mike

[Radian]

I guess this is radiators only? Your return temperature spends most of its time below 50^oC which is good but the cycling suggests they're controlled by TRV's so even at minimum modulation the boiler is delivering something like double the amount of energy required. Have you looked at other variables like pump speed? Reducing the speed might extend the run time a bit.

[Temp]

Looks like the cycle is about 45-48 mins, so something like 30m burn 18min off. That looks very good to me.

 

You could experiment with both faster and slower pump speeds to and see what happens.

 

You might also try setting a higher "Flow Temperature Desired". This appears to be acting more like a "Maximum Flow Temperature". You might find the boiler fires up for longer because it takes longer to get to that maximum.

[Temp]

We fitted smaller jets to reduce the output of our oil boiler but i dont know if thats possible for gas boilers.

[PiMike]

3 hours ago, Radian said:

I guess this is radiators only? Your return temperature spends most of its time below 50^oC which is good but the cycling suggests they're controlled by TRV's so even at minimum modulation the boiler is delivering something like double the amount of energy required. Have you looked at other variables like pump speed? Reducing the speed might extend the run time a bit.

There's only one TRV in use and it's in a bedroom so on low. I think I need to reduce d.0 a bit. The pump is on speed 2 so I could play with that, or even try the proportional settings. So many variables ...

 

Mike

[PiMike]

1 hour ago, Temp said:

We fitted smaller jets to reduce the output of our oil boiler but i dont know if thats possible for gas boilers.

I can reduce the boiler output with the d.0 setting. 12kW is clearly too much for CH at this time of year.

 

Mike

[Radian]

2 hours ago, PiMike said:

There's only one TRV in use and it's in a bedroom so on low. I think I need to reduce d.0 a bit. The pump is on speed 2 so I could play with that, or even try the proportional settings. So many variables ...

 

Mike

As you probably know, range ratting it down will only restrict the maximum modulation value. This will make it take longer to reach the point at which it cycles off but what about your DHW? You might need the 12kW to get a decent reheat.

Why have you settled on a 55^oC flow temperature? If you go lower, the boiler controller will self-impose a lower modulation level from the get-go and leave 12kW available for DHW (which I assume has its own flow temperature)

[PiMike]

I'm experimenting With flow temp. 55C was a starting point. DHW has its own max flow temp and power rating (d.77 from memory) which I left at 18kW. The burner always fires at 63% at the start of CH demand regardless of the d.0 setting.

 

Mike