New boiler not always getting up to temperature

[bluezee]

Evening all,

We had a new boiler fitted a few months ago. Vaillant ecoTec plus 430.

First few weeks it worked great, rads were baking hot, as was hot water.

Then I think I had to bleed one of the rads, system lost some pressure. I topped it up, but it was reluctant to get up to temperature for a while. Rads would get warm but not hot. Hot water wouldn't get quite as hot so would run out quicker.

After a while it seemed to settle down, rads and water were nice and hot again.

However, we just had some decorating done and I had to remove a rad. Put it back in yesterday day, bled and filled the system back up to 2 bar.

And now it's happened again! Boiler seems confused and reluctant to give it the full beans for a sustained period!

Seems to be something to do with the computer brain that controls it?

It's running off a traditional on/off stat rather than a fancy vaillant "modulating" one and I have heard that can be an issue? Maybe I need to bite the bullet and upgrade? Don't imagine it's straightforward wiring it up though?

Thanks for any help and advice anyone can offer.

 

[Hairymelon]

Is there a bypass and is it slightly open ?

 

[Jurassicspark]

What's the temperature set at?

Does the boiler reach that temperature? If it does display the desired temperature on the display and the radiators don't get hot as they should then you've got a problem.

If it doesn't fire till the desired temperature then this can be normal (most of the time).

Are the radiators properly balanced?

 

[Stuckinarut]

Wiring up should be easy enough, but not a diy job when removing the boiler cover. I wonder if it’s getting airlocked?

 

[bluezee]

Typically, after a week of playing up, it decided to get it's act together just after I posted the above

But it just seems sensitive, quite likely it gets unsettled again tomorrow and bounces around at 40-45 degrees again.

It's set to 65 and as of right now, it's purring away at all even temp.

I did reset it...

I don't think it's anything to do with the overall system, rads etc, as when it's happy it works perfectly, everything gets very hot. Seems like more of an electronic issue?

Not sure if there's a bypass, where would I look?

Don't think it's getting air locked, no strange noises (think there would be?)

Maybe I need to look into getting the matching vaillant controls fitted.

 

[Madrab]

Topping up to 2 bar is too high - 1.5bar at the most.

 

[Johntheo5]

Evening all,

We had a new boiler fitted a few months ago. Vaillant ecoTec plus 430.

First few weeks it worked great, rads were baking hot, as was hot water.

Then I think I had to bleed one of the rads, system lost some pressure. I topped it up, but it was reluctant to get up to temperature for a while. Rads would get warm but not hot. Hot water wouldn't get quite as hot so would run out quicker.

After a while it seemed to settle down, rads and water were nice and hot again.

However, we just had some decorating done and I had to remove a rad. Put it back in yesterday day, bled and filled the system back up to 2 bar.

And now it's happened again! Boiler seems confused and reluctant to give it the full beans for a sustained period!

Seems to be something to do with the computer brain that controls it?

It's running off a traditional on/off stat rather than a fancy vaillant "modulating" one and I have heard that can be an issue? Maybe I need to bite the bullet and upgrade? Don't imagine it's straightforward wiring it up though?

Thanks for any help and advice anyone can offer.

Have a look at the diagnostic "D" codes, Flow/return temps, D40/D41, if the dT between these is greater than ~ 25C then the boiler may ramp down in output, if its cycling on/off then the flow temperature is exceeding its SP by +5C, this can be caused by poor circulation due to sludge in the system or/and, the boiler minimum output is greater than the heat demand.
What pump and setting have you got?, does it show the power in watts, W?, some also show the flowrate in m3/hr, either or both very useful in trouble shooting.

 

[bluezee]

Thanks, how do I put it in diagnostic mode?

I tried pressing + and - buttons together, that activated "chimney sweep" mode, it then fired up and ramped up to 115 degrees(!) before shutting down. I don't imagine that's what's supposed to happen?

I'll have a look at the pump and report back.

I don't imagine it's sludge as they flushed the system when fitting it a few months ago. He said the system was very clean.

Strange thing is when it's happy and settled it works great, just seems to be a very fine balance, slight variation in flow or pressure maybe and it backs off but no error codes on the screen.

 

[bluezee]

Update! It's cooled down so I reset it and cranked the stat up so it stops confusing it. After a few minutes of thinking the boiler fired up to 65 and is holding steady.

My theory:

It seems that the stat we have (Honeywell wireless thingy) is trying to be clever as well.

I think what's happening is when the temperature starts to approach the target (on the stat) it stops calling the boiler (early) but...

It seems the boiler also does this, i.e. it seems to interpret the stat's on/off and fire up/down based on the pattern of on/off signals from the stat.

I think basically they're confusing each other if that makes sense?!

Maybe I just need to get a simple "off when temp reached" stat that sends the boiler a clearer signal.

Or perhaps there's a way to configure the stat to use a less clever mode.

Hmm checked stat manual, it has "fuzzy logic" (sounds like the problem to me!) and can't be disabled.

Boiler is happy as day now with stat turned right up, ticking over at 65, everything hot, so doesn't seem like a system issue, must be the stat?

 

[bluezee]

Perhaps this is the issue? Maybe I just need to turn the boiler anti cycling time right down so it does what the stat wants rather than "thinking" about it?

 

[Johntheo5]

Don't know how to access the D parameters.
Re anti cycle time, D.02, the default setting is 20 minutes BUT if you look at the anticycle time (Look up) table, you will see that 20 minutes with a boiler target temp of 65C gives a actual anticycle time of 4.5 minutes, if the target temp is 55C then the actual anticycle time is 8 minutes, I would say you certainly require that anticycle time of 4.5 minutes to allow the flow temperature to fall sufficiently to allow the boiler to get away in one go after the burner refires.

What make/model of roomstat do you have?.

 

[bluezee]

Thanks @Johntheo5, well, not really knowing what I'm doing, I hacked my way into the installer menu and knocked the anti cycle time down from 20 mins to the minimum setting of 2 mins I think, and... After a few hours, tbh, it does seem to have solved the problem. Stat is maintaining a steady 21 degrees now, boiler is doing what it's told and coming on when the stat says.

Before it just seemed to be all over the place, stat would be calling for heat but the boiler would be languishing at 40 degrees and definitely seemed to take longer than 4.5 minutes to wake up, often it seemed to just get stuck, maybe stat still trying to switch on and off kept knocking the timer back to the start.

TL;DR seems to be working fine now! Though what you're saying makes sense. Guess I'll just see how it goes from here. Thanks again.