Vaillant oddity

Harry Bloomfield · 4 Oct 2019

Here is my installation..

Vaillant ECOfit Pure 418 18Kw
VR 65 Control Module & VR10 cylinder sensor
VRC 470F Controller + VR 21 Outdoor sensor/DCF77 receiver + Radio Receiver in boiler.
Sunvic SDM 1901 3-port
Hercol 117L 0.44 Sq M cylinder.
Grunfos Alpha + Circulation pump, variable speed
Open vented.

This is a regular occurrence...
Heating system enabled by time, but not the HW.
Boiler sometimes fires up when there no call for heat, runs for a very short period, then shuts down. Usually radiators don't become warm, just warmed up very slightly.

It happened this afternoon, 470 was registering 19.5C indoors, 12.1C outdoors, with the desired set at 16.5C. Living room radiator temperature increased to 23.1C.

Its not causing a problem at all, when heat is actually needed - it works absolutely perfectly as it should - all is new, apart from the pipes and radiator panels. I'm just curious to know what's going on.

Mottie · 4 Oct 2019

How long has the boiler been fitted?

Edit: Ignore that, just looked up and I see you have Vaillant controls.

When I had my Vaillant Ecotec Plus 418 18kw fitted, I had similar problems from day one. While I was waiting for the engineer to come back, I phoned up Vaillant. Before I could even finish explaining they asked me if I had Vaillant controls. I said no and straight away I was told that Vaillant controls work on 24 volts and if you use any other controls, you have to remove the 24v link from the circuit board. I said it was a Vaillant installer that installed it but they said it’s the most common fault on new boiler instals. I removed the link myself and cancelled the installer. Been fine since.

DP · 5 Oct 2019

deleted

Harry Bloomfield · 5 Oct 2019

Motman said:
How long has the boiler been fitted?

Edit: Ignore that, just looked up and I see you have Vaillant controls.

18 months the boiler, but installed with my old very basic controls

I swapped the controls to the Vaillant kit, last March.

Even on the basic controls I would hear the boiler run an unnecessary purge cycle in the last year's summer, as though it were about to fire up. I continued to notice that since changing the controls this year, but as the outdoor temperature has fallen, now it seems to actually fire up.

I did get in touch with Vaillant soon after the boiler was installed and they claimed not to know what it might be doing when it ran a purge cycle. They suggested I checked the display for any error codes, but it has never presented with any errors at all.

I am no wondering if it might be doing some prediction that it will soon need to actually fire, so its pre-empting that need by doing a short burn cycle to pre-heat the water in my heating system.

Mottie · 5 Oct 2019

Harry Bloomfield said:
18 months the boiler, but installed with my old very basic controls

I swapped the controls to the Vaillant kit, last March.

Was the link removed when it was first installed? If so, was it refitted when Vaillant controls were used?

Harry Bloomfield · 5 Oct 2019

I'm not sure, but I do remember reading up on that link and ensuring I followed what ever the advice was. I'll check later..

Harry Bloomfield · 12 Oct 2019

Motman said:
Was the link removed when it was first installed? If so, was it refitted when Vaillant controls were used?

I have just had a look and...

B. OFF terms are linked
RT terms are linked
BUS is wired via a two core up to my VR65

There isn't a 24v terminal(s)

Harry Bloomfield · 12 Oct 2019

Anyone know, are these links correct for my system?

ScottishGasMan · 12 Oct 2019

Yes links are correct. its probably your controls that arnt. Ecofit was built years after those controls were obsolete to work with the VRC700 and VR70. Only thing that might be worth a try is checking what the S.Code is on the live monitor when it does its intermittent firing

Harry Bloomfield · 12 Oct 2019

ScottishGasMan said:
Yes links are correct. its probably your controls that arnt. Ecofit was built years after those controls were obsolete to work with the VRC700 and VR70. Only thing that might be worth a try is checking what the S.Code is on the live monitor when it does its intermittent firing

Vaillant asked me to check the S code, the boiler wasn't reporting any faults.

In fact the boiler seemed to run an occasional what seemed to be just a purge cycle without actually burning, before I added those Vaillant controls.

Its installed in the kitchen, in a cupboard and runs almost silent, so its rare that I actually catch it misbehaving like this. I guess it does it maybe once every few days..

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Vaillant oddity

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