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?

 

[Rystar00]

Sorry Riley!

I have the vsmart which comprises of a VR65 wiring centre and a separate room stat (comes in the same box)

 

[Riley]

I'm reckoning wiring fault did Vaillant guy check wiring

 

[Stoney Ground]

We then tricked the boiler when it was heating hot water to heat the rads instead (at 70 degrees with burner on max) by manually opening the motorised zone valve. All of the radiators (bar a couple that had dodgy valves which we've now fixed) and all the rads were roasting. So the pipe work and rads are fine.

By doing what I said in post 45, 3 weeks ago you would have proved this.

 

[Riley]

I'd get Vaillant back mate you've proven the system works

 

[Rystar00]

Thanks Riley - I will get them back. They said to change the range rating on the boiler downwards but that's had no effect. I understand from searching other forums that I'm not the first to have had this problem.

Stoned Ground - fantastic advice thank you. I showed your post to my installer (he probably hates me now!) and he followed those instructions to identify the issue.

I will keep you posted on what happens next.

 

[Stoney Ground]

Sometimes it's easier to take away external controls to prove they are or aren't the problem. Maybe ask Vaillant to send a senior technician they need to prove to you there is not a fault with their system.

Have they tried a full factory reset of boiler and controls?

 

[Rystar00]

I thought it might help if I took the boiler from 'auto' under the heating load to the actual load.

I have calculated my rad heat output as 18,137kw so how much should I allow for my unvented cylinder please? 2kw? Would it then be a good idea to set the heating load at 22kw?

Thanks again guys!

 

[Riley]

Right you've proven that your radiators get hot yes ?
You did this by essentially taking the zone valve out of the equation?
I think you are looking at a control or a wiring issue
I'm not sure that there is a kilowatt loadage issue

 

[Rystar00]

Hi Riley,

Thanks again for your support. Your advice has been incredibly helpful and generous.

Yes we have established that the rads get hot (by manually opening the zone valve when the boiler 'thought' it was heating hot water) so the installer agrees and thinks it's a wiring/control issue.

I thought adjusting the load might help as I wonder if the boiler is going into anti-cycling mode too quickly if its oversized? It's probably something as simple as the wiring or controls but I've read other forums that have posts with similar problems to mine and that's what they suggested.

 

[Riley]

Have you got Vaillant coming back I think you are just clutching at straws a bit at the moment mate you need to go at this with a plan rather than just randomly changing stuff in the hope that it will fix it. My suspicion would be that there is an issue with the wiring centre

 

[Rystar00]

Yes mate - they're coming out on Monday.

Ok will gladly follow your advice and leave well alone this weekend. Will keep this thread updated once they've visited.

 

[ShaunCorbs]

Thank you for keeping us updated and I wouldn't think changing the kw setting of it would matter too much

 

[Last Plumber]

I've just skim read all this so excuse me if I cover something that has been dealt with or if i've missed the point entirely and please do not take offence at anything. Like I say it's a massive thread and I may have missed vital parts of the conversation.

If that Heating MV when opened manually, allows the heating to work, Why has It not been changed or at least inspected ? How do you know the paddle or ball isn't broken or clogged ?

I have seen the rubber ball type swell once due to heat and also once due to an overdose of inhibitor. That would give the symptoms you describe.

Also I did not see what the rads are made of but if they are cast iron, could it be casting sand left inside that has got washed out and into the MV ?

I'd remove that MV and look !

I know it opens manually which would indicate it is not blocked but they don' t always open quite as far by motor .

Again, really sorry if i've missed the point here !

 

[Last Plumber]

What's the Flow and return temp on boiler ?
Both the pipe temps beneath and menu 40 and 41?

 

[Last Plumber]

Has anyone checked that the valve is not slipping on the teeth when opened by the motor.

When you open them manually you shuv the thing open regardless of teeth

 

[Last Plumber]

In fact, having had a rest and a think
My official diagnosis ( for now and If no one else has said it )
is :-

The brass cog on the MVmotor is missing teeth !.

It needs looking at.

Watch it be something completely different now to make me sound way too over confident.
I hope i'm right !

 

[ShaunCorbs]

In fact, having had a shower and preparing for my Disaronno in the plumbers arms.
My official diagnosis is :-

The brass cog on the MVmotor is missing teeth !.

It needs looking at.

Watch it be something completely different now to make me sound to over confident.
I hope i'm right !

The only thing I will say that won't keep the heating water low temp about 45dc max which is the problem

 

[Rystar00]

Thanks again guys. No problem at all Last Plumber - all input is very welcome and I'm extremely grateful for it! This place is an amazing resource.

The installer took apart the MRV and the heating lockshield and it was all absolutely clear. He didn't note any problems with the teeth.

 

[Last Plumber]

MMMM I'm trying to catch up a bit here so bare with me whilst brain catches up with fingers !

I know Vaillant start and run low sometimes depending on flow rates and I ve seen them run a good few minutes before picking up speed. I was thinking that if the valve was slipping it would be opening and closing but you're right. That would not account for constant temp.
I see OP has added that the MV was checked too.

It just seems odd that when the boiler runs and the valve is opened manually, the heating works well, which points to the valve and rules out pipe probs.

We all know that the thing opens and causes (via whatever method ) the heating to come on.
If it opens and switches the boiler on, then the Micro switch works too. It can only be a circulation problem to do with the valve. The boiler and DHW circuit work well I believe.

Do you or OP know what the flow and return temps are ?

If you can't get them off pipes, ( which would be best ) you can get them from 40 and 41 its just that that includes the slip from the bypass and can be misleading.

Sorry to waffle, I'm typing and thinking at the same time.

Never know, it may make someone else hit on the answer !

 

[cjpb]

Hi all,
I've just signed up since I've been having the exact same problem.
I live in the north of Portugal, not the UK though.
So I've had a Vaillant Plus combi boiler and the vSmart thermostat installed about a week ago.
This is on a 3 bedroom apartment with 6 radiators plus a smaller one in the bathroom.
The installer set the CH water temperature to 75ºC and with the vSmart disconnected the boiler works fine. All the radiators warm up and the apartment gets heated quickly.
The vSmart was not installed at the same time since it's not available in Portugal yet. Had to get it shipped from Spain. I did check that I had a netatmo weather station nearby and I've since confirmed the outside temperature is spot on. This also means that I'm left by myself to get it to work properly.

So after everything is connected (the app works fine) I would set the thermostat to 20ºC (outside temperature 12ºC, room temperature 18ºC) and the boiler would start. The flow temperature would get to ~43-44ºC and the boiler would enter anti-cycling constantly (FT would get as low as 35). Changing the boiler settings (eg max output) did not make a difference. At this temperature the radiators are not able to warm the house. Hot water works fine by the way.

So after reading many posts in several internet forums I was convinced it had to do with the weather compensation function. I had a look at the manual of the vrc470f which is available in Portugal. On page 50 you have the heating curve diagram.

If the vSmart uses a similar formula, with a heating curve of 2.5 (default was 2.6) and an outside temperature of 12.5ºC the flow temperature should go up to 45ºC which is very close to what I get.
Unfortunately this is not enough the warm the apartment.
So I tried setting the heating curve to the max (5) and it got warm really fast Now I've been reducing the setting (4.5 at the moment) to find the sweet spot. Perhaps if I had left it in auto it would have found the best setting after a week or so (?) but frankly it's cold and I don't want to wait for that long to see if it sorts it self out.

It seems the heating curve is best fit to really cold weather, well insulated homes (mine needs improvements for sure) and perhaps efficient radiators (low temperature? mine are 20 years old).

So my advice to others complaining from poor heating is to ramp up the heating curve then slowly get it down to find the best compromise.

regards,
Carlos

 

[MatthewHurt]

Sorry but I don't have time to read the previous 109 comments so dont know of this has been said, but if you're using g VSmart controls with anything other than a combi then you will need a Vaillant wiring center, assuming that you have one of these fitted and all is wired correctly, get Group Service to come back to it. It could be an issue with the PCB not recognising the Ebus input (will show in the Dcodes)

If you put the hot water on and manually open the heating zone valve then the rads should heat up, this will prove that the pipework is OK and has no blockages (although you may still find issues heating the index circuit especially if the HW is on because the internal pump is likely to be too small for your home).

The VR66 wiring center also has a fault indicator light inside which may give a clue as to whether there is an Ebus comms issue.