Vaillant Boiler not warming enough

[dilalio]

Okay mate, thanks. I'll try the air bleeding and let you know how I get on. Cheers

Your boiler measures the temp of the return water back from your radiator circuit, and uses this to determine if it should keep firing.
If there are restrictions in this circuit (due to air/ sediment/ balancing - or any way that the path can short circuit) the boiler will cycle to try and maintain a baseline temp between flow and return. It's like Cruise Control for your central heating.

 

[ripperuk]

Thanks very much for your help.

I've checked, but there is no air in the system as water comes out. I did look at the balancing, but this is not possible, because part of the procedure is to put the boiler on max setting and measure the temperature with a thermometer, but my boiler after reaching max drops temp again, so I won't be able to get a correct reading for each radiator.

You mentioned sediment and I'm thinking if balancing because of the way the boiler is currently functioning, whether I should do the flushing option first???

 

[dilalio]

Don't try and get too technical about it all, at this stage! Try and get the rads to feel (to the touch) the same temp, by closing down lockshield valves by a 1/4 turn at a time, on the hottest rads, and opening them up on the coldest!
Take heads of any thermostatic valves and make sure the pins have movement and are not stuck. If you find a rad or two that won't get hot, try shutting down all others to force flow through just that rad. This can be used to get sludge back in suspension and carried around the system, before resorting to more drastic forms of flushing!

 

[simond]

Steelmasons is right on the money. 5 pages and his post is all you need.

The Mk2 ecoTEC, in all its plastic glory, has some 'clever' software that makes assumptions on flow and return temperatures.

If an installer, for example, fits a 637 (37Kw in out of the box default mode) to undersized pipework (very, very, common), the Mk2 ecoTEC versions will cycle at around 50-55C due to the fast temperature rise in the water circuit being interpreted as a warm house.

The way round this is to either spec the pipework correctly (ho, ho) or tell the boiler it is a smaller model by altering the d settings.

With larger combination boiler models the heating is normally oversized leading to these problems. An experienced Vaillant installer would know of this, as it has been the case for the last 5 years, since the launch of the push button facia.

 

[Steelmasons]

It's like talking to a brick wall @ times Simond...

 

[ripperuk]

Steelmasons is right on the money. 5 pages and his post is all you need.

The Mk2 ecoTEC, in all its plastic glory, has some 'clever' software that makes assumptions on flow and return temperatures.

If an installer, for example, fits a 637 (37Kw in out of the box default mode) to undersized pipework (very, very, common), the Mk2 ecoTEC versions will cycle at around 50-55C due to the fast temperature rise in the water circuit being interpreted as a warm house.

The way round this is to either spec the pipework correctly (ho, ho) or tell the boiler it is a smaller model by altering the d settings.

With larger combination boiler models the heating is normally oversized leading to these problems. An experienced Vaillant installer would know of this, as it has been the case for the last 5 years, since the launch of the push button facia.

I don't disagree with any of Steelmasons posts as I think he's spot-on, but I've tried the both the 18kw & 30kw setting and the same thing is still happening, where the water warms upto 75C and then quickly drops to 60C and then cycles back up to 75C etc. That's why I've looked at other options, such as the radiators themselves. They are slightly over luke-warm to touch.

 

[simond]

Get someone to check the internal bypass.

 

[Steelmasons]

Change d.000 to 10kw and work from there..

 

[dilalio]

or any way that the path can short circuit)

 

[The831Bunny]

What controls have you got? The boiler MAY be reducing the flow temperature due to modulation. Most Vaillant controls can be set to adjust the flow temperature. If standard controls then valves wide open on a towel rail, or an external separate bypass can cause this as many have correctly mentioned.

Also seen this on systems with all TRVs of dubious quality only partially opening. From all your info Kw input is set too high and/or you have a circulation restriction....

 

[ripperuk]

Guys, firstly thank you for all your help. It's much appreciated.

@simond - Internal bypass?

@dilalio - I've just done the radiator balancing. I turned off all radiator valves and then turned the valves either a quarter or half or even full depending on how cool/hot they were. I've definitely noticed a massive improvement in the radiators and they are much hotter than before, so thank you.

@Steelmasons - As picture below shows, I've now changed to 10KW - But could you please kindly explain why setting the kw lower would make the boiler work for longer and what changing this setting exactly means? :-

@The831Bunny - Apologies, but I don't know what modulation is. The boiler has the controls shown in the picture above. The radiators have TRV & Return valves.

 

[Agile]

That behaviour can be caused by a seriously unbalanced situation where a rad close to the boiler is taking all the flow.

It is not possible to set up the boiler until the rad's have been properly balanced.

Tony

 

[Steelmasons]

Hey ripper , it must be your lucky day as you have the831bunny taking the time to post on this thread...
He's been working on vaillants before the dinosaur went extinct , take heed of what he says...

 

[Steelmasons]

What are the readings in d.040/d.041 when burner shuts down?

 

[ripperuk]

@Agile - I've done the rebalancing.

@Steelmasons - Which part of the831bunny's post are you referring to mate that I need to take heed?

Also how long shall I run the boiler/CH before getting these readings and would I need switch off the room thermostat (to force the burner to shutdown) and then get the reading?