I have a Vaillant TURBOmax Plus. Both the HW and CH are intermittently cutting out with error S.33, check air/flue system. I powered it up and watched the air pressure switch signal, D.24, it was not changing state, i.e. D.24 = 0. I can hear the fan going and the fact that the problem is intermittent implies that the flue is not blocked. I was going to test the air switch electrically, by removing it, but then I noticed that the boiler sometimes cuts out with error S.07, pump over run. Might these problems be related? Would somebody explain pump over run to me, please.
Vaillant Turbomax Plus, S.33 (Air/Flue) and S.07 (Pump Over)
- Thread starter NoNoNotDIY
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Firstly the S codes are status codes, not fault codes (they are F codes). A status code simply tells you what the boiler thinks it's doing at that particular moment.
Pump overrun is a normal situation that occurs after boiler firing and allows any residual heat to be dissipated.
Perhaps you'd like to reconsider your post bearing in mind the above?
Pump overrun is a normal situation that occurs after boiler firing and allows any residual heat to be dissipated.
Perhaps you'd like to reconsider your post bearing in mind the above?
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The air pressure switch on the Vaillant has a reputation for failing, as it is not a particularly expensive item, and is easy to access I suggest you change this, then wait and see.NoNoNotDIY said:
Chrishutt - thank you for your quick response and apologies for my terminology. I was working on the basis that any status where a boiler is not boiling, must be erroneous. 
Any more information on pump over run? Why is there residual heat, when the boiler has only just fired up? How long would it normally stay in this status? Next time it happens, I'll just leave it and see; but it seems to remain in this status indefinitely.
meldrew's_mate - Thanks, good tip. Not the only Vaillant part that has a reputation for failing; my Diverter Valve went last year.
Any more information on pump over run? Why is there residual heat, when the boiler has only just fired up? How long would it normally stay in this status? Next time it happens, I'll just leave it and see; but it seems to remain in this status indefinitely.meldrew's_mate - Thanks, good tip. Not the only Vaillant part that has a reputation for failing; my Diverter Valve went last year.
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The diverter valve usually fails within 2-3 years and the APS within a further 6-9 months.
Whenever I change either I explain the symptoms of the next fault to the owner. Being able to predict the next fault and obviously knowing how to repair it means we are always called to the next breakdown.
Tony
Whenever I change either I explain the symptoms of the next fault to the owner. Being able to predict the next fault and obviously knowing how to repair it means we are always called to the next breakdown.
Tony
The "not particularly expensive" post put me in mind of a few quid, under a tenner. I just got quoted £49.64.
Found one on the net for just under £30.
Any advances?
I don't mind paying this, if it works.
I just wanted to check that it's what you pros would pay.
Found one on the net for just under £30.
Any advances?
I don't mind paying this, if it works.
I just wanted to check that it's what you pros would pay.
I think the trade price for a spare would be around £40, so £30 sounds OK. You could try www.abcotuk.co.uk - they do cheap generic spares.
At that price I'm hoping the APS is going to fix the boiler, install itself and make its own tea.
To kick off the debate, the boiler was installed in March '02. So the Vaillant part has an average lifespan of 4 years (okay, only one sample).
Could a cheaper part be any worse?
By the way, no one has satisfactorily explained Pump Over Run, yet.
To kick off the debate, the boiler was installed in March '02. So the Vaillant part has an average lifespan of 4 years (okay, only one sample).
Could a cheaper part be any worse?
By the way, no one has satisfactorily explained Pump Over Run, yet.
Sorry, didn't mean to sound critical. I should be asking more specific questions.
So, at the risk of askign dumb questions...
What should be happening during a Pump Over Run?
Should the pump be running?
What causes a Pump Over Run?
Where does this "residual heat" get dissipated to?
Why is there residual heat? Surely any heat is useful heat that should get pumped around the CH.
Why is it called Pump Over Run? (I ask this question in half jest)
Over Run, to me, implies some kind of failure condition; like overload or overpressure. But hey, never assume anything, right?
So, at the risk of askign dumb questions...
What should be happening during a Pump Over Run?
Should the pump be running?
What causes a Pump Over Run?
Where does this "residual heat" get dissipated to?
Why is there residual heat? Surely any heat is useful heat that should get pumped around the CH.
Why is it called Pump Over Run? (I ask this question in half jest)
Over Run, to me, implies some kind of failure condition; like overload or overpressure. But hey, never assume anything, right?
Hi, my Turbomax plus also does S.07 pump over run, absolutely normal after it has been running the boiler. I'm guessing that it's setup to ensure that the heat gets evenly distributed around the system after the boiler has been on so that the heat exchanger doesn't sit there really hot after heating demand and loose the heat into the boiler when it could usefully be transferred into the rads (as per your point 5).
There's also the possibility that its there to ensure that the heat exchanger cools down in a more controlled way after heat demand, so as to reduce the effects of rapid heating and cooling.
Whatever it's function, it appears to be absolutely normal, you're wondering why there should be residual heat after the boiler had fired up and then shut down immediately, it's possible that the engineers didn't take that into account and there is a set time for the pump to run after the boiler has run, no matter how long the boiler has run.
Chrishutts "never assume anything" is the first rule, check it again and get seven independent witnesses, but also try not to be distracted by something that doesn't appear to have anything to do with the problem that you're trying to solve.
Hope that the APS replacement fixes your problem.
There's also the possibility that its there to ensure that the heat exchanger cools down in a more controlled way after heat demand, so as to reduce the effects of rapid heating and cooling.
Whatever it's function, it appears to be absolutely normal, you're wondering why there should be residual heat after the boiler had fired up and then shut down immediately, it's possible that the engineers didn't take that into account and there is a set time for the pump to run after the boiler has run, no matter how long the boiler has run.
Chrishutts "never assume anything" is the first rule, check it again and get seven independent witnesses, but also try not to be distracted by something that doesn't appear to have anything to do with the problem that you're trying to solve.
Hope that the APS replacement fixes your problem.
Cheers guys, you've all been a great help.
I'll let you know as soon as I've replaced the APS, which is likely to be after the weekend.
I'll let you know as soon as I've replaced the APS, which is likely to be after the weekend.
Yep! New APS solved the problem.
Now I have to put the cupboard back together; the previous DIYer built the cupboard such that the door frame had to come off to get the cover of the boiler off.
Thanks again.
Now I have to put the cupboard back together; the previous DIYer built the cupboard such that the door frame had to come off to get the cover of the boiler off.
Thanks again.
I've just been seaching the web as I've had the S33 problem for a year. I had an engineer out twice who replaced the Diverter Valve but did not sort the problem out. Sounds like, reading your thread, that it most likely is the Air Pressure Switch. Is this straightforward to replace?? Just pull out the 2 tubes and 2 electrical wires and replace?? The manual seems to suggest that I have to fiddle with lots of valves etc?! Is ity a DIY task for a novice??
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