Vaillant Ecotec Plus - Pump overrun when restarting

Sorry for the confusion. On our specific installation the boiler doesn't act as a combi. Only the second temperature knob gets used as far as I understand. I will try heating at 66-70 to see if it makes a difference. But thought it was more energy efficient to stay on a low temperature which is why I was always on 55.
 
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A boiler, regardless of configuration, is still a heat generator. Have used a combi as a Y or S plan often. Combi supplies water to kitchen sink, cylinder to the bathroom. :p
 
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Thanks again for all your responses. The way our boiler is installed, all the hot water (kitchen + bathroom + everywhere else) comes from the water tank. I'm not 100% sure about the model. I think it's 428 but I will have to double check this evening.
 
Its not a combi but a heat only boiler.

Even so the boiler needs to be set to at least 10 C above the setting of the cylinder stat.

Cylinders should be set to 55-60 C so the boiler at 65 - 70 C.

Unfortunately your boiler model is rather simple and will not accept a single input to cause it to switch its output temperature.

Tony
 
Thanks
I checked with 65 and still getting the bug. I have an engineer coming on Friday. Will let you know what he thinks.
 
From the start up sequence that's a 400 series ecoTec. The heat input is too high for the system and/or the circulation is poor. How many radiators are on the system and what pump was recently fitted, also what is the size/age/type of your house the boiler is installed in?
 
Hi
I have 12 radiators (some being quite small) and a water tank. But the thing is I still get the same bug when only the HW is switched on on (ie flow only goes to 5 radiators plus tank). Actually the bug is even more pronounced when only the HW is on. The pump is a alpha2L 15-50 130.
House is quite old with a mixture of old and new radiators. The new radiators are 6-8 years old and so is the boiler. It's a 3 floors house with loft and rear extension. The boiler was fitted when the rear extension was built (few years after the loft extension). Hope this helps
 
Hi
I have 12 radiators (some being quite small) and a water tank. But the thing is I still get the same bug when only the HW is switched on on (ie flow only goes to 5 radiators plus tank). Actually the bug is even more pronounced when only the HW is on. The pump is a alpha2L 15-50 130.
House is quite old with a mixture of old and new radiators. The new radiators are 6-8 years old and so is the boiler. It's a 3 floors house with loft and rear extension. The boiler was fitted when the rear extension was built (few years after the loft extension). Hope this helps
Ok, firstly there is no bug. The pump is too small, a 6M head (15-60) is the minimum requirement, possibly a higher head pump than a 15-60 is needed, it depends on how the system has been piped. Although swapping the pump for a higher head model to try and compensate incorrectly sized pipework can lead to other problems like pumping over etc etc. So I'd recommend a proper heating engineer takes a look who is conversant with Vaillant boilers. Firstly though there are two things that need to be checked.

Alpha pumps modulate, and cause reduced flow problems with most low water content/high resistance heat exchangers. Fixing the speed of the pump on lll should give you the best available performance from your current pump at least. More than likely is been left on the auto setting.

The heat input is probably set at maximum at the boiler too, if it is a 428 that will be 28Kw. Check D.0 (see boiler instructions), I'd advise reducing to 16Kw for starters. Try these couple of things first and let us know if things improve.
 
Thanks. Pump is already on III. The d.0 setting is something I had already changed previously. It improves things a lot but doesn't remove the pump overrun issue completely.
Is there a way I can check the amount of water that gets into the boiler to see if the pump doesn't pump enough?
Let's also see what the engineer says tomorrow. Thanks again all for your help.
 
Thanks. Pump is already on III. The d.0 setting is something I had already changed previously. It improves things a lot but doesn't remove the pump overrun issue completely.
Is there a way I can check the amount of water that gets into the boiler to see if the pump doesn't pump enough?
Let's also see what the engineer says tomorrow. Thanks again all for your help.

Hi. Wrong pump setting was top of the 'probability' list, but hey ho!

There's absolutely no benefit from setting the boiler to output more heat than what the radiators are rated at. As a rule of thumb, with the correct circulation and a balanced system the temperature difference between flow (D.40) and return (D.41) at the boiler should be between 15-20C. That equates to approx 1.5Kw per radiator for an average insulated house.

Open all TRVs to full, run the heating only. Check D40 & D.41 when the boiler has reached 60C+. Reduce D.0 till you have 15-20C difference. If that figure (in KW) is less than your radiator requirement there is a restriction on the system. Your engineer then has to discover where this is....
 
Thanks. Pump is already on III. The d.0 setting is something I had already changed previously. It improves things a lot but doesn't remove the pump overrun issue completely.
Is there a way I can check the amount of water that gets into the boiler to see if the pump doesn't pump enough?
Let's also see what the engineer says tomorrow. Thanks again all for your help.

When you are talking to experts who might be able to help you, the first thing to do is to tell us EVERYTHING and that includes what your current d0 setting is left at.

You don't seem to be able to understand that your system is full of water all the time and and the same water just circulates round the system.

Tony
 
Sorry for that. When doing the video on the first post the d.0 was 25. I will try to reduce tomorrow to see how it goes.
 
Hi All
Just to give you an update. I had an engineer coming last week. He came up with pretty much the same diagnostic - "system working properly".
I now have the d.0 at 10 and temperature at 65 degrees. With these settings it almost works fine. Sometimes the boiler switches off a bit more quickly than I would expect but it always works long enough so we get the hot water to a decent temperature. Of course I still can not make a "hot restart" too quickly but it is probably as good as it can be.
Thanks all for your help. It has been very helpful.
Teebob
 

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