Vaillant ectotec Cycling Problem

[ALEC1]

i think compensated boilers are designed with a different understanding....and I dont think that understanding is readily available in the UK..

 

[Jamer]

Point taken about system design. It could be my issue.
But I'm having trouble understanding why the heat differential is ok when I limit the output to 14kw, but the system doesn't modulate the output back automatically. Surely it should read the temps coming back in are rising, suggesting that the rads are equalising with desired room temp and compensate slowly. As it is, it keeps banging out heat until she 'cannae take any more'. Am I being especially dim today?

 

[Dan Robinson]

Jesus, why can't people start their own threads... are we dealing with a 4 or a 6 series here now?

 

[ALEC1]

Jamer...... I would set the controller up to act as thermostat... this does modulate the flow temperature down and eventually shut the boiler down when room target room temperature is reached.

However its worth reading this blog which was started by a client of mine:

http://vaillantcyclingproblem.blogspot.co.uk

Dan there are real issues with in the installer community about adopting and understanding this technology...as you have seen in the combustion chamber. Put frankly until the well respected and much loved interested people such as you and Gaswizard ask the "naysayers" to shut up while we discuss the subject then this forum isn't the place for us to trade experiences. Never the less many members of the public have good understanding as to how heating systems work and the snippets of information do come out here...albeit in a disordered fashion...


You have part of the key... use it!

 

[Dan Robinson]

Alec, cone on bud,you can't call any of us naysayers just because we try and look at all options. With these faults it is the assumption that the boiler is to blame.

No one has asked if the system is suitable.

Microbore, undersized pipes....well insulated and what sized emmittets? Let's look at those possibilities as well.

 

[ALEC1]

Dan I didn't call you a nay sayer... I called you



a well respected, much loved interested person...

 

[ALEC1]

and on the point of system design.. I do have a house with weather comp and some micro bore and it works fine, surprisingly...

and the house doesn't even have to be particularly well insulated!

 

[Dan Robinson]

and on the point of system design.. I do have a house with weather comp and some micro bore and it works fine, surprisingly...

and the house doesn't even have to be particularly well insulated!

Me too, but I also have customers where it works perfectly, does what it is supposed to. But because they want a room temperature of 23 and the system isn't designed for it the weather comp is useless for 2 months or so as the min outside temp is set to 5 degrees otherwise the system can't cope.

Anyway... I digress.

In every case I can think of including the one I have been asked to drive 200 miles to investigate by the boiler manufacturer today; AND on one or two of my own installs... Pump sizing is the cause, and/or preexisting undersized pipes.

 

[JonCa]

One work around if the pipe work is too small is to install a manual bypass between the flow and return cracked open very slightly to allow some flow to trickle through and raise the return temperature a bit. I'll get shouted at for saying that because it's a bit of a bodge, but there you go.

Almost sounds like a Low Loss Header but with almost nil capacity.

From other threads it seems the larger domestic boilers suffer these cycling probs could this be a fix?

 

[scoobydo123]

Tony and others are forgetting that this boiler fires @80% for 50 seconds regardless of d.0 (stupid emission control logic to keep NOx levels low) So statements that it is heating up in 1 minute when only set to 10kw are not true. It is actually firing at 22.4 which you dont have much chance of getting rid of if it has already raised the temp and run out of modulation bandwidth.

Gaswizard on one of your installations are you sure it doesn't misbehave when heating the cylinder? Consider say a 1/3 draw off boiler fires and gets up to target flow then starts modulating down to d.0 inevitably the boiler will cycle. Boiler will then re-fire at 80% of max load but you have all this latent heat in primaries and surrounding the coil in the cylinder ie stored water near 65c and you will struggle to get enough heat away. You are then left with a boiler that is cycling on off until eventually cylinder states is satisfied much longer than the equivalent glow worm that starts low and works up to d.0 rather than the rabbit way. Haven't worked out the water content on a coil plus piping but if you do the calcs I reckon you can see where I am coming from. Especially evident on fast recovery cylinders you never get your rated recovery as the last few degrees take a long time as you end up with a boiler only firing for around 10 seconds.

Interested in your pump in series much cheaper than a 25/80 have you literally put them one after the other without cavitation?

Any comments more than welcome

 

[scoobydo123]

Also remember that they have released a revised board (believe only 2 people in the country have it). Assume this is just a revised code on the eprom that appears to have resolved the issue and you can now use low flow temps. Try to get them to admit to it is difficult, I did ask whether it had been approved by GC but never got an answer or if approval was even required.

 

[gaswizzard]

Interested in your pump in series much cheaper than a 25/80 have you literally put them one after the other without cavitation?

Any comments more than welcome

What would lead you to believe that cavitation would be an issue?

 

[ALEC1]

lso remember that they have released a revised board (believe only 2 people in the country have it)

Yes this is correct...and it does solve the issue which I highlighted (micro firing) and everyone else thought was a pump sizing issue...

 

[scoobydo123]

Dont know anything about fluid dynamics so had to ask the question. Had in my mind that there may be disturbance with 2 circulators in series, but if it works then could be a resolution. Far easier would be to release the board for those with the problem. I have never had s.53 errors but from day oneI have suffered (perhaps 95% of all installs do when in DHW mode?) with a far from ideal system with micro-firing

. I have purchased the full WC kit but havent risked getting it installed as it is in a rented property that I pay the bills and I think I would be getting a lot of calls saying the heating isn't working properly due to the micro-firing.

What are the calc for 2 circulators in series on 22m pipe with the resistance of the boiler? Currently getting 20L of flow would this make enough of a difference to push it to burn for another 40 seconds?

Just cannot understand the logic behind the burn at 85% of max rating for 50 seconds. Can understand from a stone cold boiler but not when the the combustion chamber is already hot.

If GW or ALEC is in my area (RM7) one time I really would like you to have a look.

Thanks

 

[scoobydo123]

did the op ever get to the bottom of this? I notice that honeywell controls were being used maybe the cm series with TP control this will almost certainly clash with the boiler logic. I have the new board in mine and it behaves much better. Still like to see the behaviour of one with a standard board after the first cycle when reheating a cylinder. Luckily I have quite a large heating coil, a more modest one would really suffer I believe.