Can you solve my Vaillant combi boiler problem, Sherlock?

[Gasguru]

Actually Tony I was hoping that you and the other experts might be able to diagnose it - that is why Im posting! No need to be patronising. This is not a jet engine or an super-computer ffs - its a f*****g boiler. Whilst I would never seek to denigrate the skills of heating engineers, lets face it, there are a finite number of things that could be wrong and from the information I have given it must be possible to narrow it down to say 2 or 3 problems. I read a lot of ppl saying these Vaillants are so complicated only Vaillant ppl can do it - but I dont buy it frankly. Its a boiler. It works on exactly the same principles as all other combi boilers. If you know boilers, give me a list of what could be the trouble. Based on the empirical evidence I bet its a short list.

Grimly

Now your just talking out your a**e .... this boiler does NOT work the same principles as most other boilers.

It uses hydraulics and pnuematics in a way no other manufacture does. If its as simple as you think to repair why havn't you sussed it yet. Phone around tomorrow - I guarantee most installers will want to replace it. Only a fraction of 1% of registered installers will be prepared to repair it, the knowledge just isn't out there. The boilers are old and the experience (that solves most boiler faults) has now been lost.

Due to the way this boiler operates investigating faults often takes far longer - there are many more components that can cause potential problems and when it comes down to it many customers are not prepared to except the repair is not a 5 minute job and don't want to pay.

 

[Agile]

Diagnosing boiler faults professionally is not just a matter of having a list of possible causes ( unless you work for BG ).

Its a matter of carying out diagnostic tests on the various components and watching how they respond during the start up sequence.

If you understand electronics and have the correct mental processing abilities then its not that difficult but the hard facts that less than 1 in 20 people trying to fix boilers can even use a multimeter let alone understand what impedance is !

The people who give advice here are probably all within the top 100 boiler repair engineers in the country.

Its the facts of life ! Ask your fellow what current to expect with a stalled fan has a resistance of 42 ohms and an inductance of 0.2 H and 230v applied and he will probably blink twice and say he does not know what you are talking about !!!

Tony

 

[DP]

Tony fail to see the need to find current flow in a stalled fan. One would be able to SEE the fan is not turning so need to bring out a multimeter to measure current flow would be pointless.

 

[Grimly Feendish]

Thanks for this! For the top 100 boiler engineers in the country (per Tony's last post) you are pretty short on ideas. As for Tony's approach to diagnostics, I am sorry but I just dont agree. Diagnostics is not confined to boiler repairs; logical principles are applied to every diagnostic scenario whatever the discipline. Here, I have provided (in my first post) very clear factual evidence on the boiler's performance. That information allows experienced people to immediately EXCLUDE certain common problems. As I have said, this is not a super-computer, and however much you may want to mystify the process and talk up your own skills (or disguise your lack of them), the upshot is that there is a finite number of elements that could be malfunctioning to produce this particular problem. It is a simple matter to produce a list of what the possible causes could be. That applies to cars, computers, rockets and domestic boilers. It sounds to me that you guys simply dont know enough and are trying to mask your lack of knowledge by the classic technique of pleading extreme complexity. I dont accept it. If you cannot suggest any possible causes, then I guarantee that I will be able to track down the cause myself - in time - by a process of elimination. Whether that mandates a new boiler or an economical repair - we shall see.

Yours with some disappointment

Grimly

 

[werewolf]

Grimly

Things to check

1 Flow rate at tap.

The new h/exchanger may be less restrictive than older model so give higher flow rate.I also doubt if your engineer changed the inside of the diverter valve and attended to mod to pcb.hopefully he did.

2 Gas pressure at burner and gas rate of boiler.

These are the basic checks your rgi should have done. never had to replace pcb due to this fault.Also don`t get many problems with ntc`s on this boiler.

personaaly think it`s a flow rate imbalance.

Work on these quite a bit ,good boiler,just a little over engineered.

Hope this helps

Paul

 

[Grimly Feendish]

Thanks Paul. That's really helpful. My installer did do the modification to the diverter valve when installing the new he but I dont know about the modification to the pcb - I'll check with him. The flow from the taps is pretty much the same now as it was before the replaced he, does that indicate a gas problem as most likely? There is in fact a dial to turn down the flow rate which was seized but I managed to get it going and turned it down to minimum - again no noticeable difference.

Thanks v much

Grimly

 

[Agile]

The flow from the taps is pretty much the same now as it was before the replaced he, does that indicate a gas problem as most likely?

Unfortunately yet again you are just using vague words which have no scientific meaning.

To logically diagnose boiler faults ( rather than just keep blindly changing parts ) its necessary to make meaningful measurements. The Gas rate, DHW flow rate and the temperatures within the boiler are all information which are a competent engineer is likely to require together with the resistance value of the sensors.

I appreciate that you have such a low opinion of boiler engineers but just changing parts to see if thats the cause is not something a true professional does.

Tony

 

[Grimly Feendish]

Tony, I certainly do not have a low opinion of boiler engineers; I rather got the impression that you have a low impression of poor fools like me who are at the mercy of boiler engineers and dont want to get ripped off. No, I know nothing about the science, but I do know about logical analysis and inductive reasoning. The point I was making is that the new HE has made no difference at all to the volume of water coming out of the taps - surely something can be concluded from that (eg the old HE was not scaled up so limescale is not my problem??).

You post on this forum all the time; you obviously know boilers inside out. Paul has taken a stab at identifying possible problems which would produce the VERY SPECIFIC symptoms my boiler is experiencing. Why dont you do the same? What could be causing the problem? Make a list!

If you cant be bothered I well understand.

Grimly

 

[werewolf]

Grimly

Just read your OP and you said the flow was powerful-how powerful?.The flow rates for this boiler were not great -about 10/11 min approx.
Was the water temp. defective before the dhw h/ exchanger replaced?
The burner on these fire up at ignition rate then ramp up to full burner pressure ( about 5mbar) via a pressure pump which loads the gas valve.You could see this happen if you watch the flame picture.
With the tap on does the dhw flow from the boiler get hot?.Do you have a mixer shower fitted to sytem? Can get showers passing cold thereby reducing dhw temp.
Without getting basics covered as earlier post said gonna be impossible to give definitive answer.

Paul

 

[Agile]

I am very sympathetic to the problems that "poor fools" ( your words, not mine! ) have as a result of the two problems in our industry, low boiler repair skills and the tendancy of a few to overcharge.

We try to be totally honest with our customers and we do most repairs at a fixed cost however long that takes. We diagnose the exact part which is at fault and replace just that one part. We dont just change bits at the customers expense in case it cures the fault.

I find it quite enjoyable diagnosing faults on boilers and particularly so when several others have tried first and failed.

However, they way I work is to do tests on the appliance to logically deduce what the problem is. That requires measurements of critical parameters and we are not getting that essential information in your case and not even the most basic DHW flow rate that my 13 y.o. daughter could measure using things in the kitchen and her watch.

There is no point in my listing the parts in your boiler which could be at fault because almost anything apart from the fan and APS could be the cause. In any case I dont work like that! I pinpoint the exact part!

Tony

 

[Grimly Feendish]

Paul, thanks for this.

I'm not sure I can answer all your questions but....

1. You ask how powerful is/was the flow. It is VERY powerful - I would say surprisingly so for a hot water tap, and it is hard for me to see how a litte device like the DHW HE could get any real heat into it at that rate of flow. The best way I can describe it is that it is almost as strong as the cold tap.

2. I'm afraid I dont understand your comments about flow rates and 10/11 minimum. Presumably this can be measured?

3. There has been no change at all to the power of flow through taps following swapping the HE.

4. The DHW outlet gets warm with the tap full on, but it takes its time, and it takes ludicrously long for the luke warm water to travel the 3 metres from the boiler to the kitchen hot tap.

5. There is no mixer shower. It just services the kitchen, bathroom handbasin and bath. Oh, and its connected to my washing machine too, but Ive noticed that the boiler doesnt fire up when the washing machine demands water.

Hope this clarifies things!

Thanks v much.

Grimly

 

[Grimly Feendish]

Tony, lets try this then. Please list for me the diagnostic information I can get my plumber (CORGI registered of course!) mate to provide which will help you solve the problem. You mentioned flow rate - I can find that out. What else?

Thanks v much

Grimly

 

[namsag]

As werewolf has pointed out a couple of times to get correct temp rise into hotwater the hot tap should only be passing approx 9 litres a minute other wise the heat cannot get transfered into it by the heat exchanger. Flow rate can be adjusted by turning down the isolating tap on the cold supply to boiler (located under boiler) seeing a your adjuster on water section has seized
As for board modification during heat ex replacement that all depends wether it is a hybrid board, there was also a modificatin done on theses boilers which had something to do with pressure on gas valve.

 

[Grimly Feendish]

Thanks Namsag, tbh I was confused about the whole flow rate thing. So I can measure the flow rate and if its higher than between 9-11 litres per minute I have identified a potential cause of the problem, which can be fixed by restricting the valve on the cw feed? I shall try it tonight.

Thanks v much.

grimly

 

[Scrufflepeck]

Grimly, turning down the cold water feed into the boiler could be dangerous - it could cause a catastrophic combustion chamber failure (and possible serious injury or death) at worst, or at best a new boiler, if you have an undiagnosed gas or combustion issue.

From what Ive read I would get a new boiler anyway - yours is old, knackered and obsolete. Modern boilers are mostly rubbish but at least you get a guarantee. Also, 243 output is pretty low by todays standards. Wickes and B&Q do cheap combis and Ive not heard of any serious complaints about them - no more than Vaillant or Bosch/Worcester anyway. I reckon u could get a nice condensing boiler replacement, with power flush thrown in, for £1200 plus VAT max fitted and commisioned.

Of course, your real problem is that you've got a combi - I hate them! I doubly hate condensing combis which do exactly what it doesnt say on the tin. Fine for underfloor heating where the return temp to boiler is low, rubbish for trad CH where return temp is high. Waste of money. Get a Rayburn and have an immersion heater backup!

Al