Vaillant ecoTech plus 418

26 Jan 2006
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United Kingdom
This question centers around setting 'D70' on this boiler, which should give either DHW priority when set at '0' or allow CH and DHW to operate together when set at '1'. However, it does not seem to have any effect, as DHW has priority at either setting. Copied below is an edited copy of an e-mail I sent to Vaillant Technical, which explains the situation more fully. They have not have any of you guys had a probem like this?

I have an occurrence (won’t call it a problem but may be it is.) that I hope you can help with.
The boiler is a two year old Vaillant echoTech plus 418, until recently using generic controls in an ‘S’ system, which performed faultlessly using two ancient MOMO valves. I fitted a VRT360f controller, VR65 and VR10 in Unistor to upgrade the system. The valves were replaced with spring return Honywel 2-port 4043H valves. I now find that with ‘d70’ at boiler set to either ‘1’ or ‘0’ (yes I did hold the (i) button for 5 seconds until it stopped flashing) the boiler operates with DHW priority over CH in either case. Both boiler controls are set fully clockwise.
This is what is occurring in practice:-
The CH is programmed to activate ON at 06:30 and the DHW at 07:00.
At 06:30 the CH runs normally at a steady flow rate of 75ºC, as set on the boiler, as long as the room temperature demand setting of 21ºC is not achieved. At 07:00, the DHW demand is made by the VRT360f, signified by the flashing tap symbol on the boiler display, and the boiler flame immediately shuts down. After a short pause, the boiler reignites, then cycles quite rapidly until the set DHW of 60ºC is achieved. When checked physically, by feeling valve leaver resistance, the CH valve is definitely closed and the DHW valve is open whilst the boiler is cycling, irrespective of boiler ‘d70’ setting. During last month, when only DHW was activated, boiler operated normally, heating water as required. The system is operating satisfactorily, with cylinder water maintained at correct temperature. Just don’t understand why DHW seems to shut down CH despite ‘d70’ setting being at ‘1’ and causing the boiler to operate for only short periods (cycling) which it doesn't do when only DHW or CH is demanded via VRT360f. Worried that cycling will shorten the life of the gas valve etc. What do you make of this situation, if anything?
Thank you in anticipation
Peter H Kay.
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You have a situation which will need someone with considerable experience of setting and operating your combination of products. On this forum that may well be Gas4U or 831 Bunney now that Dangermouse has been restricted from giving advice.

Its always possible that its operating correctly within its design parameters.

One thing that I would point out, which may overcome your problem, is that its normal to program HW heat up BEFORE the CH in the morning.

Vaillant has apparently abandoned any meaningful technical help so dont expect any reply to your email or to telephone calls. The nature of your call is so detailed that its unlikely that any of them would know the answer without doing tests on any installed equipment. Thats one of the downsides of using near state of the art equipment.

Vaillant lack of help is so pronounced that its difficult to conclude that it is caused by any inability to respond but would appear to be a management decision to force installers away from their products. They are part of a large group with other brand names and possibly want to reduce the significant market share that Vaillant has in the UK.

Have you checked what happens if you set d70 to 2?

Won't be the first time I've seen faulty VR65's :mad:
Thank you both 'Gas4you' and 'Agile' for your replies. This morning I have disconnected the VR10 thermistor from the NTC position in the VR65 and fitted a cylinder thermostat, connected to its correct location in the VR65.
A DHW demand still shuts the boiler down for a short period, if it is responding to a CH demand, but when it reignites both valves now remain open with D70 set at '1'. The cycling has also ceased. I just wish I knew what the VR 65 is doing with the signal from the VR10 NTC.
This situation now opens another 'can of worms'. The instruction manual for the VRT360f does not differentiate between having a VR10 installed or a standard cylinder thermostat for the DHW. In fact, it doesn't mention either. It just states that both the DHW and room temperature can be set at the VRT360f without any proviso.
How the hell does the boiler know the temperature of the DHW if the VR10 is not giving it this information via the VR65? Similarly, the cylinder thermostat will open and close when the DHW is above or below its set temperature, irrespective of the setting on the VRT360f. This system has me completely baffled and I now wish I had saved my money and kept the original Drayton SCR1 and mechanicaly programmed timer At least I could understand what was happening!
Thanks again guys. Anyone else got any ideas? I suspect a copy of the programmers notes for the VRT360f would be the only way to see what should happen, as the Vaillant documentation is abysmal
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With a standard cyl stat, the boiler, or indeed any of the electronics cannot know how hot the hot water is. It is a simple on/off scenario.

That is the reason for using the VR10, as this is basically just a ntc/thermistor.

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