New Vaillant eco tec pro short cycling (Floor heating)

[justAnAccount]

Good morning

I'm having some short cycle problems with a new Vaillant eco tec pro. From a cold start it runs for about 30-40 seconds before going into its short cycle program/wait time which by default is set to 20 minutes, I have temporary set it to the minimum of 2 minutes.

Some facts that might help us with the troubleshooting:

- Total area of the apartment is 65m2 (every room has floor heating)
- There are 5 floor heating loops (each of them report between 1 - 2 liter/minutes)
- There are 2 extra loops connected each to one reserve radiator. Those 2 extra loops can be closed separately from the floor heating
- Pump speed is set to 53%
- CH temperature is set to 35C
- Requesting hot water for the shower, or other is working fine
- When the boiler is running, only the two first meter of the floor heating feels warm. The rest of the floor of the apartment is not cold, nor warm.
- A few seconds after the boiler enters its short "cycle wait time/protection" the water in the floor heating drops to room temperature

Here is what I tried:

- Completely opening, closing or set on the "right spot" the pressure relief valve (it's a manual valve not an automatic one)
- Completely opening or closing the loop from the extra radiators
- Playing with the flow valve of each loop from the floor heating
- I tried different CV w modes. By default, it is set to auto. I also tried the minimum 8W, 10W and the maximum (which is 20W or a bit more)


Thank you for the help

 

[Mottie]

Don’t know if it’s anything like the problem I had with my Vaillant eco tec pro when first installed but if you are using anything other than the Vaillant controls (that work on 24v), you have to remove the 24v link from the circuit board. Apparently it’s one of the most common faults on a new Vaillant installation…..

 

[Johntheo5]

Good morning

I'm having some short cycle problems with a new Vaillant eco tec pro. From a cold start it runs for about 30-40 seconds before going into its short cycle program/wait time which by default is set to 20 minutes, I have temporary set it to the minimum of 2 minutes.

Some facts that might help us with the troubleshooting:

- Total area of the apartment is 65m2 (every room has floor heating)
- There are 5 floor heating loops (each of them report between 1 - 2 liter/minutes)
- There are 2 extra loops connected each to one reserve radiator. Those 2 extra loops can be closed separately from the floor heating
- Pump speed is set to 53%
- CH temperature is set to 35C
- Requesting hot water for the shower, or other is working fine
- When the boiler is running, only the two first meter of the floor heating feels warm. The rest of the floor of the apartment is not cold, nor warm.
- A few seconds after the boiler enters its short "cycle wait time/protection" the water in the floor heating drops to room temperature

Here is what I tried:

- Completely opening, closing or set on the "right spot" the pressure relief valve (it's a manual valve not an automatic one)
- Completely opening or closing the loop from the extra radiators
- Playing with the flow valve of each loop from the floor heating
- I tried different CV w modes. By default, it is set to auto. I also tried the minimum 8W, 10W and the maximum (which is 20W or a bit more)


Thank you for the help

If the boiler/Ch temperature is set to 35C then IMO not a hope of getting the boiler to modulate down after fire up as it once the temperature reaches 40C (SP+5C) the burner will trip and stay out for the recycle time, you have say 5 loops X average of 1.5LPM = 7.5LPM, when the boiler fires up it will fire at ~ 65% of max output, so ~ 13kw and will not modulate down for 60 secs., the boiler temperature at fire up can,t be more than say 25C so the very max dT before the burner trips is (40-25) 15C, you would need a flowrate of at least 12.4LPM to achieve this, once it modulates don to whatever the boiler minimum output is, say 5kw then the dT will be 9.6C at your flowrate of 7.5LPM so the burner will continue to fire either continuously or for some time if the heat demand is < 5kw.
Is there a Autoimatic by pass (ABV) installed on your system?.

I would initially just increase the boiler SP to 60C and if the boiler continues to fire after say 60 secs or so very gradually reduce the SP to 40C and see how you get on.
Is your UFH fed directly from the boiler or is there another pump with a TMV (thermostatic mixing valve) on the manifold, if not then suggest, as a temporary measure increase all the loop flows to say 2.5LPM and carry out a few more tests.

You should also be able to reduce the anti cycle time, will look at the specs later.