Vaillant ecotec plus cycling on HW only demand

[gaswizzard]

there is precious little research about any heating technology in the public domain... for a reason it must be...I wonder what that is?

What do you feel you are missing out on Alec?

 

[ALEC1]

I am not missing out on anything, and am happy that I install the best solutions, which conveniently (to me and my clients at least) happens to compliment the way heating technology has been developed in Germany and Holland. I understand what the technology does and why it is that way.

Others stick with tried and tested ways, and find the adoption of some technology somewhat daunting. They ask for proof. They ask for me to substantiate what I say, despite my considerable experience with the technology.

It seems there are two sets of rules: Agile can say that micro firing does not affect overall efficiency, despite alot of us understanding that it is highly undesirable and significantly reduced with lower modulation ranges..

I then get asked for proof, but Agile does not, it smacks of double standards...thats all...

 

[gaswizzard]

despite alot of us understanding that it is highly undesirable and significantly reduced with lower modulation ranges..

Until manufactures can design a gas train that allows stable burner operaton at low loads then i'm afraid we're stuck with it , vaillants new ecotec has a 5:1 turdown ratio which is a step in the right direction (among others) , turndown ratios below 20% for mass markets is not really an option if costs are to remain reasonable.

Yes micro-fireing/cycling is undesirable but not the end of the world , with regard to low mass heat exchangers we can't expect much more , can we?

..........as for fuel wastage on ignition................................. one could possibly offset this by increasing CO2% a tad.

 

[scoobydo123]

Still trying to understand what the logic behind the boiler firing at 80% of rating of d.0. this only seems to cause issues and extended heat up times for cylinders. Without question the boiler was selected due to the capability of it modulating down to a very low figure(at the time probably the best on the market) alas only if you can get past the first 50 seconds without it overshooting which seems to be very difficult to achieve. Why was this logic employed in the 4 series does any other boiler employ the same logic?

 

[gaswizzard]

Without question the boiler was selected due to the capability of it modulating down to a very low figure(at the time probably the best on the market)

I doubt that scooby , plenty other manufactures with turndown ratios in excess of 33% (3:1) , as said before i've not had a problem with these boilers when installed correctly. you have a circulation issue period.

 

[scoobydo123]

Ok so how do I find where my circulation issue is or are you saying it is a pipework issue? Why did the technical lead engineer not blame it on poor circulation, I am very close to 20L per minute. I can only get around a 10 seconds burn (when it starts short cycling) yet first burn is extremely long and the boiler modulates as it should, when eventually it does overshoot and goes into cycling mode the fun starts. If the boiler is down rated by the fan speed adjustment it behaves better but does still overshoot during the start up sequence on occasion..


Can a domestic circulator provide much greater circulation through the restrictive heat exchanger on the 400. I have compared with an ultracom2 (30kw) on 28mm primaries and this has around 15l per minute.

 

[GuessMan]

Hooooooooow long is this bleating thread going to run?

Alpha's new boiler has a reported turn down ratio of 1:8, not sure if that's true on the open vented model though. Why not get one of those?

 

[gaswizzard]

If the boiler is down rated by the fan speed adjustment it behaves better but does still overshoot during the start up sequence on occasion..

.

I've had the same issues with a 428 , the only way to resolve the problem was to fit a 25/80 circulator (not my install) and all was fine.

20 l/m is around 2.3 metre head loss through the boiler , with a 15/60 fitted ths leaves around 3 metre head for primary pipework losses , it doesn't take a genius to work it out.

Have you confimed primary pipework into coil is not partially blocked? , use a magnet to check or better still disconnect the pipework at cylinder coil , what is the flow rate through boiler when CH is calling?

 

[The831Bunny]

+1 GW. As I said on page 1, that's page 1 of this thread, a 15-60 is a minimum requirement. Depends on the system, as you say...

I'll pop by and post in the Autumn again

 

[scoobydo123]

Guessman I am not about to install a new boiler as it does work just not as well as it should.

It has a 15/60 (Grundfos) and this did not seem to make much difference (replaced a British gas branded circulator). Haven't checked for build up but will of course. Not got any figures for CH only. Interesting about the different circulator, was you getting only around a 10 second burn and this managed to extend it to the 50 seconds for it to start to be able to modulate? So I have a 6m head pump, the header tank is around 1.5M from the top of the boiler (from memory) with the pump and motorised valves about 1.2M below the boiler. Not sure if this helps with any calcs or theories.

Gaswizard what area do you cover? Need to get someone in who knows what they are talking about wasn't that happy with the engineers that visited they thought there wasn't a problem and where quite happy with it during the initial fire but couldn't understand what was going on during the initial 50 seconds of subsequent fires.

Do really appreciate all the advice given.

 

[gazdaz36]

Fitting a low loss header might improve flow through the boiler and keep it running long enough to modulate down.

 

[scoobydo123]

Gazdaz looked at how much the low loss header is and I think it might be a bit cost prohibitive. If it didn't cure the issue then I am back to square one. Thanks anyway

 

[Dan Robinson]

Buy another one or make one.

 

[scoobydo123]

If I was able to make one then I think I am going to struggle for a place to site it (boiler is in the kitchen with valves an circulator in a cupboard below that it only 310mm deep so everything is packed in quite tight (this is also the meter location). Or could I just put it on the cylinder that may well have the room? Thanks.

The other idea was to put a radiator on the DHW primaries and mount in the cupboard where the megaflo is sited and then insulate this thus increasing the volume of water for the DHW primaries. Thing is then this would make the cupboard a bit warm in the summer and also not be the most energy efficient I guess.