Vaillant Ecotec 831 problems

[JSHarris]

Hi,

We had an Ecotec 831 installed around 4 years ago, to replace an ancient wall mounted boiler. The improvement in efficiency (and much reduced gas bill) was welcome, but the thing has been very unreliable, with the dreaded F75 fault being a very regular occurrence each winter, and seemingly unfixable by those who've tried - all the engineers who've looked at it have said that sometimes these boilers just do this.

The boiler developed leaks from the rubber hoses shortly after installation (fixed under warranty by fitting new hose clips), the diverter valve started leaking a year ago and was replaced (the shaft seal had failed) and now the boiler has developed another fault that keeps the heating on all the time.

At this point I'm wondering whether to call the engineer in yet again, or scrap the boiler and get something that will work reliably (absolutely not another one from Vaillant!), as I get the feeling I'm now throwing good money after bad.

The symptoms of the latest fault are that, usually after a power interruption (we get occasional power cuts here), the boiler will get stuck into running the central heating all the time, even if the room programmable thermostat is physically disconnected (I can unplug it from the wall). The hot water still operates normally, with the boiler switching between heating and hot water as normal, the boiler displays no fault codes and the information display confirms that there is no heating demand from the room thermostat. The heating flow temperature is being controlled correctly - I can turn it down (it's normally set for 48 deg C) and the boiler responds correctly.

Even with no heating demand from the room thermostat the boiler keeps running the heating, unless I turn the heating flow temperature dial to zero (although as mentioned above, the display confirms that there is no heating demand, showing S.0 or S.30 ). Resetting the boiler (which is often needed to overcome the frequent F75 faults) seems to have no effect, but if I turn the boiler power off, leave it for a while to cool right down, then power it on again it will sometimes fix the problem and all will be OK for a while.

I suspect that there may be a (probably very expensive) fault with the main circuit board now. If so, then given the probable cost of replacing this I really should think about scrapping this 4 year old boiler and getting one that won't need constant repair and attention.

My question is, does my diagnosis of an expensive circuit board fault seem likely, or is there a chance that this problem could be caused by another, potentially less expensive to fix, problem? I'm reluctant to get the engineer around yet again, as the fault can be difficult to reproduce once the boiler is working OK, and I suspect I'll just be into another round of very expensive "suck it and see" parts replacements.

So far the boiler has cost around double the original installation cost in repairs and failed in some way around 50 to 60 times, so it's not exactly on my list of reliable appliances!

 

[Agile]

Whilst certain models do have common faults like your leaking rubber tubes and occasional diverter valve failures, your model is generally reliable and well worth while repairing.

The F75 fault is very well known and usually caused primarily by dirt in the system. Any competent engineer should have no problem fixing it. I do wonder if your usual engineer is very good at repairs, not all engineers are! Many specialise in the more lucrative installation work.

It could well be the PCB and a good way to get a great deal is to engage British Gas on a fixed price basis or possibly Vaillant. I am surprised that you have not taken out their cover before!

Tony Glazier

 

[JSHarris]

Many thanks for the swift reply. I've had two engineers look at the F75 problem now, the original installers (who did try their best but ended up as frustrated as I am) and another local chap who seemed to know his stuff but again was foxed by the problem.

The system was power flushed when the new boiler was installed and is fitted with a filter in the return to the boiler. It's had inhibitor in always and this has been checked regularly (usually during the many repair visits). When the diverter valve seal failed last year the old parts came out looking clean and the consensus was that dirt probably wasn't the cause of the ongoing F75 problem (the pressure sensor has also looked clean each time that's been replaced). They were both of the view that the boiler just suffered from this problem in some installations and nothing really could be done about it. I think they both felt it was a design fault that Vaillant wouldn't own up to!

Thanks for confirming the probable cause as being the PCB, it makes deciding what to do a little easier. I agree, I should have gone for a fixed price servicing agreement, but having been used to the solid reliability of our 20 year old boiler (which never ever failed in any way) I kept thinking that each repair would be the last! It seems that modern boilers just aren't intended to be reliable or last for more than a few years, judging from the plethora of stories around of failures.

The annoying things is that this boiler was strongly recommended as being one of the most reliable at the time we had it fitted; it's been galling to wake up in the morning so many times with no heating or hot water.

 

[Agile]

Put it this way, some of the engineers contributing to answers here actually work for Vaillant and repair their boilers all week!

Some may answer here! I would be surprised if they do not agree with me that the F75 fault can always be repaired. Sometimes it will reoccur months later and the same repair procedures need to be repeated.

The dirt is not on the sensor ( except in extreme cases ), its in the areas behind the sensor and a bit fiddly to get to.

Apart from the rubber hoses and diverters your boiler is one of the most reliable on the market.

Tony

 

[ianmcd]

I would contact Vaillant customer services and be polite and express your concerns ASK what they would suggest to resolve your problem, you have a very decent boiler and I certainly wouldnt get shot of it, Vaillant are a decent company and if you get the right person on the phone they might repair for free as its only 4 years old and they did offer a 5 year warranty on these for accredited installers, but although you are very frustrated dont make the mistake of venting your anger at the manufacturer or they will just blame your installer and walk away, also with this model I wouldnt be cutting the power to turn it off as you stated as this can cause damage to the boiler

 

[JSHarris]

Thanks once again for the valuable replies. It's nice to know that the advice I originally received about the reliability and performance of this boiler was correct, but galling to have experienced so many failures, pretty much from the time it was first installed. I think the hoses started leaking within a couple of months of the boiler being fitted and the F75 fault has always been present, right from the first week. It's now become predictable, if the weather turns cold overnight, after a mild day before so that the system has cooled right down overnight, then the boiler will pretty much always throw an F75 fault first thing in the morning, needing one or two resets to get it to fire, or occasionally a small pressure top up from the filling loop (the pressure doesn't drop over time, so there is a limit to how often I can do this before having to get the system drained a bit).

Once fired the fault then doesn't recur until the next combination of a mild day followed by a cold night. If I shut off around half of the radiators manually the night before cold weather is forecast (they have TRVs) then I can always prevent the fault occurring. The engineers and I have jointly concluded that my system has a very low flow resistance when all the TRVs are open and this is enough to prevent the kick from the pump being reliability detected. Whether we're right or not I don't know, but the evidence seems to suggest we may be. At least this means I can now manage the F75 problem, as long as the weather forecast is right!

To be honest I've long since stopped being angry about this, and have become resigned to the fact that it's just an unreliable and costly bit of kit. I know that the original installer did have some lengthy conversations with Vaillant about the F75 problem, and tried all their suggested fixes, like replacing the pressure sensor, cleaning the internal filter etc. I think I've now had four pressure sensors, although replacing them hasn't had any effect on the problem. The original pressure sensor was replaced under warranty, as it was acknowledged to have a manufacturing problem, but the warranty I was given was only for 12 months and all the other repairs have had to be paid for. I've not once felt that the engineers weren't trying their best to fix the problem, though, they have always seemed as frustrated as me about it. I gave up trying to get the F75 problem fixed a couple of years ago, and have just been living with it, as there seemed little merit in calling out an engineer yet again.

I will follow that very useful suggestion of going direct to Vaillant, and see what they have to say. If I could get the boiler working properly and learn to trust it as being reliable, then I may be prepared to keep it. It does work very well when it's working, plenty of hot water, excellent heating performance and much lower gas consumption than the old Potterton it replaced.

 

[Agile]

When operating the CH do you know what the flow and trturn temperatures are?

Or just feeling with your hands on the CH pipes under the boiler how hot does each one feel?

Tony

 

[JSHarris]

As it happens, I've had sensors fitted to these pipes and connected to a data logger. We super-insulated the house, by degrees, over the past few years, so significantly reducing the heating requirements, which allowed me to turn the flow temperature down in an attempt to keep the boiler running in full condensing mode more of the time.

Currently the flow temperature is set at 48 deg C, but delivered at around 46 deg C, and the return is usually around 40 to 42 deg C once the system has stabilised. The boiler seems to modulate down to maintain this at the moment (hard to tell for sure, as my version doesn't have the modulation level display - it just sounds as if it's burning more quietly). I have had the flow temperature as high as about 55 deg C in very cold weather (for example, when the outside temperature is below freezing for a day or two) and then the return temperature tends to increase slightly to around 45 to 48 deg C and the system operates with a higher differential, as would be expected.

I've effectively ended up with oversize radiators now, as they were sized for the heating requirement when the house was built, back in the early 80's. This does work to our advantage now, though, as it means I can run lower water temperatures and still get the heat we need.

 

[Agile]

Thats a differential of only 5-6 C whereas the boiler is usually used with a differential of 15-20 C. Although at such a low flow temperature the usual operating parameters are not usually the same.

The engineer suggested to you that the system resistance may be too low. With such a low differential that could well be the case!

I would suggest that balancing to give a higher differential may help to stop the F75. You could almost do that yourself by closing each lockshield by say a quarter turn.

As that would reduce the average rad temp it will be necessary to increase the flow temperature a little to maintain the same heat output.

Nice to see someone who protects the planet ( and their own bank balance ) by adding good insulation!

Tony

 

[JSHarris]

Thanks very much for the tip about balancing, it'd not occurred to me before, as when we had TRVs fitted all the LSVs were wound wide open, in the belief that the TRVs would balance the system (which indeed seems to be the case). What you say makes perfect sense though, as when the temperature drops overnight all the TRVs will be wide open, lowering the flow resistance. I'll have a go at opening all the TRVs, manually balancing the rads and then setting the TRVs again. I can pretty much remember which rads were throttled down the most from when we had the old boiler and no TRVs (they were fitted at the same time that the boiler was changed, at the insistence of the installer who said it was a mandatory requirement now).

All the advice received when looking at the F.75 problem previously was that this boiler is inherently fairly sensitive, and that the tiny pressure kick it looks for at pump start is difficult to detect in some installations. Even when starting normally it usually has at least two goes before it ignites, as it invariably fails to detect the first pump kick. I think in our case the problem is exacerbated by having relatively short, fairly straight pipe runs, the house being single storey and the boiler being the highest point in the system.

The interesting thing is that in all the years we had the old boiler I had no idea what was inside the case, it just worked. All it ever had was a service, usually when I was at work. Since having this boiler I've learned a lot about exactly how it works, simply because it's spent many hours with it's covers off whilst various engineers have struggled (often in vain) to fix it!

FWIW, we're in the process of planning a self-build, and that will be a passive house, with really minimal heating requirements. I'm looking forward to a house with no boiler

 

[Phill Peck]

I have an 831 it is now over 7 years old and have never experience a major problem.

F75 Is probably the easiest fault to fix. To completely resolve this issue there is a remodel kit. You could contact Vaillant direct or find an engineer who knows what to do.

What make is your room stat?

Danfoss stats/programmers have a surge protection that has to be reset if there is a power cut or power surge it goes to ermenantly on

 

[JSHarris]

Thanks, that's interesting about the remodel kit to fix this fault. Both the companies that have looked at this contacted Vaillant for advice, I'm sure. I remember on at least one occasion the engineer having a 'phone conversation to someone technical at Vaillant, whilst trying to get to the bottom of the F.75 problem. That was around 4 years ago, not long after the boiler was installed. I'm also sure that their advice was followed, as I believe that the original pressure sensor change, and perhaps a pump change, were a result of it. I remember thinking it odd at the time that a brand new boiler should be fitted with defective parts and that the manufacturer was recommending that they be changed.

The room stat/programmer is a Drayton Digistat 3 that is battery powered, so doesn't suffer from the effect of the mains going off. The only connection is to the boiler, just a twin cable that connects to terminals 3 and 4 on the boiler and this is just a pair of contacts on a latching relay in the 'stat that call for heat when closed.

At first I thought the new problem of the boiler staying on was just the 'stat getting stuck. I eliminated that as the cause by just unplugging it which automatically disconnects the terminals and should have shut the boiler off. This had no effect (the boiler stayed on), so I then traced the wiring back, looking for damage, thinking that there must be a short somewhere that was keeping the boiler on. The wiring looked fine, as far as I could tell (most of it runs through the roof space).

Next I turned the power off and checked between terminals 3 and 4 on the boiler with a meter, to see if there was a short, so calling for heat all the time. There wasn't, but when I turned the power back on the fault cleared. Since then I've discovered that when the boiler locks on like this - it did it again last night, we woke this morning with the bathroom like a sauna (no TRV on the towel rail!) - it can be persuaded to go back to normal by switching off the power, waiting for half an hour or so, then turning it back on. So far this has always fixed it (the fault has occurred around 6 or 8 times now). It does seem related to power cuts though, as we had a brief outage at around 10pm last night, which coincides with the boiler being on all night (the programmer/ 'stat should have turned the heating off overnight) and it wasn't calling for heat this morning when the boiler was locked on).

 

[Phill Peck]

I have had a few problems with Drayton stats.
However if the s codes are s.0 or s.30 then it would appear not to be the problem.

I would still not recommend changing the boiler.
Bu contacting Vaillant direct may be your best option at the point. They do fixed price repair regardless of how many faults or what is required.

 

[The831Bunny]

So far the boiler has cost around double the original installation cost in repairs and failed in some way around 50 to 60 times, so it's not exactly on my list of reliable appliances!

Thats got to be a wind up surely?

The cause of your problems are:
1. Bad installation, dirt in the system, inadequate flushing and/or lack of correct inhibitor. 80% of F.75s are related to carp in the boiler as are leaking DV spindles. There are other issues, but lack of correct servicing and dirty systems are top of the small list. I bet the DV isn't leaking clean water right???
2. Incorrectly diagnosed problems by visiting engineers.

If you had these problems within the 2 year warranty, then a call to Vaillant would have seen you with the upgrade kit fitted and advise on the water quality (if needed).

Possibly the DV is partially seized and staying in the Heating position and causing the rads to warm when the boiler is doing warmstart (pre-heat). Turn off the warmstart to confirm this. If and when the boiler 'stays on' press the i button instead of turning it on and off. There is no case that the heating would be on or the pump running and S.0 or S.30 are displayed.

 

[ALEC1]

I would treat yourself to a vrc 430 or 470 after the engineers visit...

Ebus controls from vaillant and their boilers are a fit for purpose match, and with over 50 boilers out there with this match, it is noticable that these controls reduce sognificantly issues...

I tend to agree, this is a good boiler and worth keeping..with vaillants controls you wont be buying a better boiler...that match is the end of the product line and you wont be nuying a better boiler...