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

[rahbar]

Same thing at the tap. 3 engineers out thus far, going to call them again now though as it must be a fault.
If anyone knows how the internals of these charging tanks work and can think of where I should point the engineer to please feel free to chip in! (I know it shouldn't be necessary, but hey, it's in my own interests I guess).
Thanks to everyone for helpful replies

 

[Agile]

Engineers dont like to be told what to do!

Best to get a no-fix no-fee as that seperates the men from the boys!

Not that many engineers will be very comfortable diagnosing the fault.

Tony

 

[mickyg]

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.

 

[Agile]

Same thing at the tap. 3 engineers out thus far, going to call them again now though as it must be a fault.

I am glad that you agree with me Mick that few are very experienced with this model!

Tony

 

[Hufty]

I'm sure someone will gleefully tell me that I'm wrong, but if I remember correctly, you need

• the aquastart C showing on the front
  AND the hot water channel of a Vaillant time control to be on or in an on time period
  AND the hot water temperature to be set to 60 or whatever at the controller

for the prewarming to work. Worth a try if it's not all on already. Think you have to press f for five seconds, tap p twice then hold down i or something, but you'll know all the ins and outs of that controller.

 

[rahbar]

Agile - lol, these are Vaillant engineers! So far they have tried to fob me off with 'its your plumbing' (30C temp loss between the boiler and the tap...I think not!). Another one claimed 'well its fine' as boiler was kicking out 60C on his meter - until I pointed out that he was not meauring the *actual* HW feed pipe the house. My point is really that sometimes it pays to have a little knowledge beforehand

mickyg - yes, same problem with taps. shower is *not* the problem - you can even feel that the water is cold if you go and touch the hw pipe coming out of the charging tank.
F75 - we've done a couple of flushes with cleaner and water is crystal clear (in fact I did a fast, hot flush then a slow one over a week). Not seen any crud, but there may have been of course.

 

[Agile]

You dont say which cleaner and for how long!

We like all the detail !

Tony

 

[Hufty]

Think you have to press f for five seconds, tap p twice then hold down i or something, but you'll know all the ins and outs of that controller.

Before anyone posts to say that I'm wrong, that was of course a little in-joke, the point being that it's not the most intuitive of controllers. And of course you are free to post that it is the most intuitive of controllers if you want to.

 

[mickyg]

lets get some facts straight about this fault then now we know its the boiler..
When the tap runs stone cold, is the boiler firing? does it display a tap symbol? does it display a flame symbol and a pump symbol(circle with a triangle inside) ? Whats the temp? If you press "i" what S code do you get.

 

[rahbar]

Hufty, I've actually developed quite a few interfaces in my time and the only words I can muster for the 937's are 'surreal'. I honestly do not know what they were thinking when they made that thing. I still keep the manual close by!

Agile, damn, I knew you'd ask that. I was feeling cheap at the time (we're renovating atm and waaaaaay overbudget as usual). It was from Selco, a standard system cleaner. I didn't feel the need to go mad as as only have 1 old double rad (ground floor), 1 old small rad (ground floor), 1 old towel rail (1st flr) and 1 new double rad (1st flr) on the system. Other rads are removed and ends capped off until works finished. Yes, it is a stupid time of year to be doing this without rads!
As I say - the when drained down the water was crystal clear before we even started any treatment.

I did 2 lots of cleaner for good measure: a quick 'after install' cleaner. Took the boiler up high and flushed it out after an hour (roughly I think).
Second lot of standard sludge cleaner was in for 1week then flushed out and replaced with inhibitor.

Sorry should have mentioned that we lowered the output of the CH side due to the low number of rads (Vaillant guy showed us this). Note that this only affects the CH - I've actually tried changing this but is has no effect on the HW problem (and its not supposed to either according to the instructions).

 

[Agile]

You will probably not be surprised to hear that I dont use cheap own brand products, only Sentinel and Fernox!

Not only do I use the best brands, but I use them consistently so that I can become familiar with their characteristics and how to get the best from them.

Largely you get what you pay for!

If I heard that a customer had used a cheap one AND I thought that treatment was needed then I would do it again with the proper one.

Tony

 

[Stamina]

tech specs on page 8

http://www.vaillant.co.uk/stepone2/data/downloads/f4/42/00/ecoTEC_plus_937_sales_brochure.pdf

 

[rahbar]

lets get some facts straight about this fault then now we know its the boiler..
When the tap runs stone cold, is the boiler firing? does it display a tap symbol? does it display a flame symbol and a pump symbol(circle with a triangle inside) ? Whats the temp? If you press "i" what S code do you get.

yes, the boiler is firing with a tap symbol. the temperature reads 63 as expected. The boiler itself appears to be working normally - you can feel the pipe coming out from the boiler itself is good and hot. However, that pipe then turns straight back and disappears into the charging tank.
However - the pipe that actually supplies the HW to the house is substantially colder.

After 10 mins or so (presumably when the charging tank is empty) water goes semi-cold at the tap (just tested at the kitchen sink). Boiler is still running as before and pushing hot water into the storage tank @ 60C, but the hw pipe coming out the supplies the house is luke warm.

 

[rahbar]

I should add my test at the kitchen sink was measured at 7.5 litre/min - well below the spec of 15l/min

 

[JoeMar]

...could be the tank charging pump is not working properly

have you checked if the pump cable (X31 and X12 - see page 33 of the installation manual) are connected properly to the PCB?