Is my Vaillant ecoTEC working properly?

[PiMike]

My ecoTec 418 was installed in 2009 with traditional Danfoss controls. I recently replaced them with a Vaillant VR65 controller and VRT2392f room thermostat. I also built an adapter so I can monitor the ebus to see what the boiler is doing.

 

I set the part load to 12kW, flow temperature (CH and HW) to 65C and room temperature to 18C. Here is a plot showing a long initial burn time then multiple shorter burns. Is that how it's supposed to be operating?

 

Thanks,

 

Mike

 

[Marvin]

Hi. My gut feeling is that the CH temp is too high, but I'm sure someone will correct me.

 

It seems to heat up very quickly and the shut down then heat up very quickly and shut down...

 

Me, I would have it at 55C and see the difference....

[MikeGrahamT21]

I agree, try 55C and see if it helps

[PiMike]

Thanks both I will try that, although that plot was made on a cold day and it's a lot warmer now so perhaps not a good comparison?

 

There was a typo in my post, the thermostat is a VRT392f.

 

Mike

Edited March 13, 2023 by PiMike

[JohnMo]

How much of the heating system is open, all of it or just a room.  To me it looks like it's short cycling after a decent run time. A short period ramping up temperature, then off time locked out repeat.

 

You need to bring the flow temp down so your return is as far below 53 deg as you can to promote condensing and improve efficiency.

 

Either make sure all your system is engaged, and or look at the installer manual and find out if you can change the ramp rate, this is the rate the boiler adds temperature, you may be able to slow this down, so you get a longer run time by slowing or extending the time it takes to 65 deg.

[PiMike]

Hi JohnMo, first a disclaimer: I'm not an expert on heating systems!

 

it's a 4-bed detached house with seven radiators currently active, one fitted with a TRV (bedroom).

 

I understand the requirement to keep the return below 55C but are you saying that a continuous run time at a lower flow temperature is better than short cycling?

 

There is no reference in the installation manual to ramp rate. Would reducing the part load have the same effect?

 

Mike

Edited March 13, 2023 by PiMike

[JohnMo]

Look at d.43 Heat curve. Mentioned on page 42 of the installer manual.  I reduced my setting (Atag boiler) and it made a big difference. Sorry called it ramp rate, instead of heating curve.

 

Here is background reading

https://tech-controllers.com/blog/heating-curve---what-is-it-and-how-to-set-it

 

[PiMike]

Ah OK, but my system doesn't have an outside teperature sensor.

 

Mike

[MikeGrahamT21]

11 hours ago, PiMike said:

Ah OK, but my system doesn't have an outside teperature sensor.

 

Mike

If you control is smart and internet connected this could do the weather compensation for you. I have Tado and mine does just that. Get in touch with them about it, remember it’s a computer and more than likely to have bugs

[PiMike]

59 minutes ago, MikeGrahamT21 said:

If you control is smart and internet connected this could do the weather compensation for you. I have Tado and mine does just that. Get in touch with them about it, remember it’s a computer and more than likely to have bugs

 

That looks interesting but the cost of converting my system would be prohibitive (even with gas prices the way they are). I've only just replaced the controllers so I'd like to get the best out of them before considering more changes.

 

I have lowered the target flow temperature to 55C and will see what difference that makes after a couple of days.

 

Mike

[SimonD]

8 hours ago, PiMike said:

 

That looks interesting but the cost of converting my system would be prohibitive (even with gas prices the way they are). I've only just replaced the controllers so I'd like to get the best out of them before considering more changes.

 

I have lowered the target flow temperature to 55C and will see what difference that makes after a couple of days.

 

Mike

 

TBH I wouldn't touch Tado with a Vaillant. It looks like you're pretty profficient with these electronics things and as far as I know, the VR65 has ebus so you can run different flow temps for ch/dhw and it allows for boiler modulation (it is very amusing that the old Ecotec 418 manual says don't use low voltage ebus connections in UK - I wonder why? - but the wiring is all there). From your graph it looks like it's installed using just relay (230V) or have you wired itall up on low voltage ebus control?

[PiMike]

Hi Simon, the VR65 is connected to (and powered by) the ebus. The VR392f is wireless with a receiver connected to the ebus at the boiler. There is an endless list of parameters that I can monitor and change remotely (including for example separate gas counters for CH and HW). Yes I can set different flow temeratures for CH and HW and as you can see in the graph above it does modulate.

 

I have two 2-port valves that are controlled directly from the VR65 but a conventional thermostat on the HW cylinder.

 

I'll put up another graph tomorrow with the CH flow set to 55C.

 

Mike

[PiMike]

Actually I'll do it now as it's looking decidedly odd.

 

I reduced the CH target flow temperature to 55C. The other parameters are:

 

HW target flow temperature: 65C

CH part load: 12kW

HW part load: 18kW

Not only is the short cycling constant but it's firing at night when it's well above the set-back temperature. I don't understand ...

 

Should I reduce the CH part load?

 

Mike

Edited March 14, 2023 by PiMike

[JohnMo]

Try setting the ch part load to minimum and see what it does.

[MikeGrahamT21]

2 hours ago, PiMike said:

Actually I'll do it now as it's looking decidedly odd.

 

I reduced the CH target flow temperature to 55C. The other parameters are:

 

HW target flow temperature: 65C

CH part load: 12kW

HW part load: 18kW

Not only is the short cycling constant but it's firing at night when it's well above the set-back temperature. I don't understand ...

 

Should I reduce the CH part load?

 

Mike

what’s the set back temperature set at and what temp does it get down to, to make the boiler fire?

 

again I can only comment on Tado, but this system if it detects temperatures falling it will act before it gets below the set point to prevent the temperature from going below, perhaps your system does something similar?

 

perhaps there’s something more fundamental at play here? Assuming it’s a modern enough boiler to have its own automatic bypass valve, you shouldn’t need one elsewhere in the system, but is there one somewhere that is perhaps bypassing at the wrong temperature? Are all your radiators functioning normally to provide some load for the boiler to heat, and not restricted too much by the lockshield?

Edited March 14, 2023 by MikeGrahamT21

[PiMike]

5 minutes ago, MikeGrahamT21 said:

what’s the set back temperature set at and what temp does it get down to, to make the boiler fire?

 

again I can only comment on Tado, but this system if it detects temperatures falling it will act before it gets below the set point to prevent the temperature from going below, perhaps your system does something similar?

 

perhaps there’s something more fundamental at play here? Assuming it’s a modern enough boiler to have its own automatic bypass valve, you shouldn’t need one elsewhere in the system, but is there one somewhere that is perhaps bypassing at the wrong temperature? Are all your radiators functioning normally to provide some load for the boiler to heat, and not restricted too much by the lockshield?

 

Hi Mike

 

The set-back is 14C and on the graph above it was firing at a room temperature of 18C. It doesn't do it every night, which is odd.

 

The boiler manual specifies an external ABV and one was fitted when the system was installed in 2009. It was replaced and adjusted last month by my heating engineer before the new Vaillant controls were fitted. All seven radiators currently in use get hot.

 

Mike

 

[SimonD]

3 hours ago, PiMike said:

Not only is the short cycling constant but it's firing at night when it's well above the set-back temperature. I don't understand ...

 

Have you read this? https://vaillantcyclingproblem.blogspot.com/p/problem.html

 

I don't know if it'll give you direct answers, but it appears to be a known problem with your boiler/controller combo

[PiMike]

10 hours ago, SimonD said:

 

Have you read this? https://vaillantcyclingproblem.blogspot.com/p/problem.html

 

I don't know if it'll give you direct answers, but it appears to be a known problem with your boiler/controller combo

 

Simon, yes I saw that a few years ago but it really applies to systems with outdoor temperature sensing.

 

I have a partial plot for today after turning the CH part load down to 5kW as JohnMo suggested. HW 5-6am, CH 6-9am. Now it's behaving at night and giving longer burns, but it turns off before the target room temperature of 18C is reached. The house is still warm though ...

 

Mike

 

[SimonD]

6 hours ago, PiMike said:

Simon, yes I saw that a few years ago but it really applies to systems with outdoor temperature sensing.

 

It also applies to:

 

Quote

In fact, we are told that it occurs more generally when modulating controls are used, including the VRT392 (which modulates boiler output based on room temperature, without taking into account the outdoor temperature).

 

Glad to see you've had some progress, with CH part load and maybe playing around with that will yield a resolution to also achieve set room temp.

[PiMike]

7 minutes ago, SimonD said:

 

It also applies to:

 

 

Glad to see you've had some progress, with CH part load and maybe playing around with that will yield a resolution to also achieve set room temp.

 

I missed that about the VRT392f because at the time I read the blog I didn't have one, so thank you.

 

I've used a number of different calculators to estimate the heat loss of our property with one bedroom in use and the answers range from 6 to 7kW. Given that the HW has its own part load setting (and it's not on at the same time as CH) then I think the original setting of 12kW for CH was far too high.

 

Final question - should the boiler stay on for the entire period of the CH programme, modulating its power as required to maintain the desired room temperature, or should it turn off periodically as mine did in the most recent graph above?

 

Thanks,

 

Mike

[JohnMo]

Good to see, you will find your gas consumption drop considerably.

 

Mine did similar to you first and second graphs, then closer to your final graph, gas consumption dropped by around 30%

[JohnMo]

What you are seeing is fine, in fact very good.

[PiMike]

That's good to know, thank you. I can measure CH gas consumption so will see what it gives in a day or two.

 

Why doesn't the boiler run until the desired room temperature is reached though?

 

Mike

[Radian]

On 13/03/2023 at 12:06, PiMike said:

I also built an adapter so I can monitor the ebus to see what the boiler is doing.

 

 

Good stuff - ebusd on a Raspberry Pi? If so you should be able to get the operational modulation value "ModulationTempDesired" which despite the name is the calculated value that's controlling the gas valve and fan. If you range rated a 24kW boiler to 12kW, for example, then this would max out at 50 (%) and if the boiler has a 4:1 modulation ratio then would go no lower than 25 (%). My Glowworm boiler is monitored via ebusd and I get this kind of spaghetti plot which shows the actual modulation bottoming out at 33% as it's only got a crappy 3:1 range:

 

 

7 hours ago, PiMike said:

Now it's behaving at night and giving longer burns, but it turns off before the target room temperature of 18C is reached. The house is still warm though ...

 

Which component is "turning off"? Do you mean the boiler is cycling off as in "hit the lowest modulation" and still too little delta?

[JohnMo]

1 hour ago, PiMike said:

Why doesn't the boiler run until the desired room temperature is reached though?

You will have a max temperature set in the control system, so the boiler slowly increases power and therefore heat output, once it hits the max temperature setting it cuts out.  It will continue circulation and when it sees the return temperature drop by a given temperature, it will kick back in to life.

 

This ramping of temperature aids efficiency as the temperature across the heat exchanger stays low for as long as possible promoting condensing as much as possible.  Condensing starts at about 56 degrees, the lower the temperature range across the heat exchanger the more condensation the more the efficiency increases.  I'm currently at about 120% efficiency consistently for UFH.