Vaillant boiler not heating radiators. Please help!

[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