Vaillant ecoTec plus 415 cutting out

[jonehboy]

Hi All,

My first post but I've been lurking in the shadows for some time!

I have a Vaillant ecoTec plus 415 boiler and its cycling on and off constantly causing the pipes to expand and contract and rattle around. The noise is driving us nuts.

From other posts, suggestions have been to lower d.0 down to match the kw outage of the rads (9kw) which we've done. Since that the boiler works perfectly when the three way valve is in the mid position, holding 66 degrees for 15-20 minutes or until the water reaches the right temp. As soon as it swings back to heating the on / off cycle begins again.

The rads get hot when the valve is in the mid position but not so hot when on the heating only option, probably due to the cycling.

My plumber believes the heat exchanger pipes could have a blockage somewhere and wants to put another chemical in to clean it. I've already paid to have the "baked bean can" air seperator removed and replaced with t sections to rule this out but could do with a second opinion before I pay out more!

(nothing personal if he reads this)

Thanks!

 

[Tibbot]

The cleaning could have done with being carried out beforehand. The heat exchangers on these are not the best for open vent systems (assuming it's the case). Worse if it's dirty is that it's non-continuous, multi-coil design makes it difficult to clean successfully as water can pass through a clear coil without needing to disturb a blocked one.

 

[jonehboy]

Thanks for the quick reply.

I'm guessing then that when on the mid position theres less resistance and it passes through a clear coil. When on heating and more resistance the water tries to go through all / both coils, some of which are blocked causing the thermal cut out.

Does that sound plausible?

I should have mentioned that some cleaner was passed through before the air seperator was removed. My plumber is suggesting some stronger stuff.

 

[Biggles..]

You have a circulation issue,if downrating on d0 fails you should also turn pump speed up if not already.failing this consider converting to a sealed system.
Last option is fit bigger pump.

Of you press the I button on your boiler you will see you have the wonderful s53.

 

[keithsb]

I have an EcoTec plus 415 and it does need a bit of tweaking to overcome any short cycling which occurs when the return temperature has not dropped low enough, before the boiler starts up again.

The problem is that during the initial 60 seconds, the power output is quite high (I think its about 12Kw).

If the return temperature has not dropped sufficiently, the flow temperature soon shoots up, and the boiler shuts off.

It then enters its anti-cycle mode, whose time is dependent on a combination of the flow temperature setting, and parameter d2.

There is a table showing the relationship between these settings, but it is not included in the manual, however it is possible to find it in one of the other EcoTec manuals.
It is called "effective boiler lockout times"

I have a copy of this table which I have used to determine the optimum setting for d2 which prevents short cycles.

Not sure if I am allowed to upload the table here?

The default for d2 is 20 minutes at 20c, this equals 6 minutes at 60c and 4.5 minutes at 65c.

The maximum time, by setting d2 to 60 minutes, is 11.5 minutes at 65c.

Try increasing the value of d2 so that the return temperature has time to drop low enough, so that when the boiler starts up, it has a chance to modulate down before the temperature gets too high.

As a matter of interest I use a flow temperature of 60c, and d2 set to 50 minutes, which gives an anti-cycle time of about 15 minutes.
This is long enough for the return temperature to drop. So that when the boiler fires again, it has time to modulate downwards before the temperature rises too high.

Keith