Vaillant EcoTec937 hot water cool after 10min...design flaw?

[JoeMar]

I have a 2 year old EcoTec937. If you run the shower all is well for the first 10 mins or so, then it seems as if the water in the charging tank seems to run out and the boiler does not seems to be able to keep up with recharging it quick enough so the water goes cold (not stone cold, but cool enough to be unpleasant for a morning shower!). The tank does seem to recharge quickly if you switch off the water for a few minutes - it just cannot keep up with any reasonable sustained flow of hot water.

has that problem only recently appeared or has it been like this since installation?

 

[mickyg]

its unlikely to be the pump as it would still provide continuous hot water with the pump not working and also pump faults usually result in 81/91 faults. I dont understand where this hot water is going. If the water is stone cold and the boiler is firing away where's the heat going???? Simple law of physics, heat energy doesnt dissapear!

 

[rahbar]

has that problem only recently appeared or has it been like this since installation?

It's relatively new, only last few months really.

I dont understand where this hot water is going. If the water is stone cold and the boiler is firing away where's the heat going???? Simple law of physics, heat energy doesnt dissapear!

Very true. But it does depend on how much of that heat is actually being transfered to the water that comes out of the hw out pipe I guess (I presume that the boiler pipe is not directly connected to the hw outlet to the property)?

Result!
Have a Vaillant engineer coming on Monday...and this time backed up by a senior one, so hopefully all shall be revealed and I'll be able to post some info about what they find.

 

[mickyg]

whats the start of your postcode? Just wondering if I know whos coming?

 

[rahbar]

whats the start of your postcode? Just wondering if I know whos coming?

SG11, presumably a few cover this area?

 

[mickyg]

haha no just one. Your 10mins from me. I'll give him a heads up

 

[rahbar]

Lol, it's a small world!!! Cool, tell him I'll make him a brew when he gets here

 

[rahbar]

have you checked to see you have the same problem from the taps? You've only mentioned the shower so far. There's no design flaw it works fine it doesnt suck in any cold water, it more or less bypasses it. There's obviously a fault with the shower or the boiler. Unfortunately some of the vaillant engineers dont get alot of of practice with these, and some fundamental design principles need to be understood to get to the bottom of some problems. I dont suspect a problem with the store pump or ntcs as they would give you intermittent F81 and F91 faults. The F75 should be rectified, and its possible you have dirt in your system thats caused it.

that's scary...looks like you where prophetic - boiler just stopped giving hot water and started showing F81/91 codes!

 

[mickyg]

if your getting F81/91 then you the NRV in the store pump may be sticking. Usually I tend to fit a new pump and remove the nrv from the new one as its not an essential component, although I'm not sure what the official vaillant line is on this so I'm not sure what will be done. Also they may change the store pcb as there was some issues with a small number causing the 81/91 due to a software error. Think you've been a bit unlucky tbh ! Anyway, I've informed the senior tech about your problems, it will be an early start for him if he comes as he lives near Ipswich so I'm sure he'll appreciate a cuppa when he arrives

 

[rahbar]

if your getting F81/91 then you the NRV in the store pump may be sticking. Usually I tend to fit a new pump and remove the nrv from the new one as its not an essential component, although I'm not sure what the official vaillant line is on this so I'm not sure what will be done. Also they may change the store pcb as there was some issues with a small number causing the 81/91 due to a software error. Think you've been a bit unlucky tbh ! Anyway, I've informed the senior tech about your problems, it will be an early start for him if he comes as he lives near Ipswich so I'm sure he'll appreciate a cuppa when he arrives

Yeah, sounds like luck has not been on our side on this one. Thanks for your help on this one, it's been driving me mad!

 

[Bunnyman]

This is a good thread Micky I look forward to senior techs diagnosis ,let's get the answer on here it's interesting

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[rahbar]

Well, it's definitely a fault, and an unusual one by the sound of it (heat not being transfered from the heating plate to the charging tank). Engineer called back to base to discuss and is coming back on Wednesday to replace a number of parts in one go as he didn't carry them as standard on the van (I think the heating plate is being replaced).

Will update with the list on Wednesday.

 

[rahbar]

We have a fix! The problem is our age old friend limescale had clogged up the heat exchanger plates that transfer heat from the boiler to the charging tanks. Engineer fitted a new set of plates and all seems to work fine now. I am still a little puzzled how on earth it managed to recharge the tanks so quickly yet not heat the water on the fly, but lets not dwell on that one because it certainly has made a huge difference.
Hopefully case closed on this one, thanks once more to all involved.

 

[Raymond999]

Hi,

I have the exact same symptoms, but on some days its all fine. I change the plate heat exchanger first, still the same problem.
I had accidently got the main PCB wet, so I changed it, still the same problem.
After a call to Vaillant (Who could not tell me much about how the PCB in the storage unit worked) I changed it, still the same problem. FYI I aslo could feel the pump in the back going on and off.
I am waiting on a new pump to arrive, but I'm not confident it will fix the problem as it felt like it was being switched on / off.

 

[muggles]

Sounds like you've spent a huge amount of money throwing parts at it without diagnosing the problem. You'd have been better off getting Vaillant out to do a fixed-price repair on it