Vaillant boiler not heating radiators. Please help!

[Rystar00]

Hi guys,

I would really appreciate your expert advice.

To cut a long story short I have recently renovated my house from top to bottom and had a new CH system installed. Key points below:

1. Vaillant Ecotec Plus 630 boiler
2. Vaillant vSMART System Controller (with a room thermostat)
3. Unvented HW cylinder
4. 13 radiators
5. 3 x towel heaters
6. 4 floors (my house is an old victorian terrace that’s narrow and short but tall!)

We had a plumber do the first fix but he badly let us down and disappeared so we asked another installer to finish the job. The second installer has commissioned the boiler.

The hot water is working absolutely fine. However the radiators are not getting hot. Some are completely cold. The system was flushed and all of the TRVs are set to fully open. Turning some of the TRVs off only has a marginal improvement on the heat output of the ones that remain on.

The installer came in to have a look and noticed the following:

1. HW demand caused the boiler to work at max output (the burner modulation graph was working maxed out and the flow temp was at 75 degrees)
2. As soon as as the demand for HW is satisfied and it turns to the CH the flow temp reduces to about 35 degrees
3. There is not much difference between the flow/return temperatures
4. Putting the room stat in the fridge didn’t cause the boiler to work harder
5. Turning off the weather compensator and running comfort mode didn’t cause the boiler to work harder

Vaillant sent an engineer out and he replaced the vSMART because of some dodgy wiring but running the same tests haven’t improved anything. He didn't stay around long enough to diagnose whether there was another problem.

I’m now absolutely desperate to get the heating working properly before it starts getting colder. Would you mind giving me a list of anything that could cause this problem (faulty boiler, faulty rads, needing a secondary pump etc) or things for the installer to try to get this fixed please?

 

[Riley]

Was it all new pipes

 

[Rystar00]

Hi Riley,

Thanks very much for helping!

Yes all new pipes - 22/15mm uponor to the rads - copper coming out of the boiler.

 

[Riley]

Is the property zoned sounds large enough to be

 

[Rystar00]

No it's only on one zone

 

[ShaunCorbs]

Sounds like weather comp is holding the boiler off

 

[Rystar00]

Thanks Shaun.

I switched off the internet so WC wasn't available, put the room stat in the fridge and put comfort override mode on and the flow temp still wasn't staying on for that long (1 minute or so at the most) - certainly not long enough for the rads to get up to temp.

I'm worried that the rads are faulty - or I need a secondary pump to circulate the hot water?

Would changing the kw settings of the boiler help?

 

[Riley]

Rads will not be faulty. Are the TRVs bi directional?
Secondary pump sounds excessive for house size
What KW is it on

 

[Rystar00]

Thanks again Riley. The TRVs are not bi-directional and all are set to max.

The KW setting is on factory auto I believe - do you think it's worth changing this (I've seen other posts where it said to do this) but I don't know enough about heating to decide what to change it to!

On a separate note the original installer hung some of the rads (column rads) on the wrong way around which meant that some of the rads weren't getting hot (as the flow pipe needs to go to the correct inlet) but the installer guessed which ones weren't on the right way and swapped these around (but we can't be sure they're now correct!). Even so some of them should still be getting hot!

 

[Riley]

That could be your answer if TRVs are on return