Vaillant Turbomax plus 828E Hot Water Problem

25 Jan 2011
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United Kingdom
I am hoping someone can help, as I have looked through this very helpful forum and nothing matches my boilers symptoms!

I have a Vaillant turbomax plus 828E and when the heating is not on and hot water is demanded the water comes out luke warm, the temperature on the display reads just under 40 deg C, and does not really change from this. However, the green light flashes and the orange light comes on, so it is seeing a demand for hot water, and you can hear the boiler starting up.

I thought it must be a diverter valve fault, but when this occurs the pipe to the central heating stays cold, so i don't think it can be this.

However, when the central heating has been on for a little while and then hot water is demanded then the water temperature is much better - although not as hot as it was a week or so ago when this fault first started.

Could this be the secondary heat exchanger being blocked up?

Any help appreciated?
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Without further diagnostic information, particularly a thermal survey, I cannot be so sure.

What do d40 and d41 read when providing hot water?

Thanks for that, I had a look into it when I got back from work and found the following.

D40 was at 32 then when I ran the hot water it rose to 38.
D41 had no value associated with it.
D7 was set at 39.

When I played with the hot water temperature control dial, turning it up to max resulted in d7 reading 50. The minimum setting made d7 equal to 20.

So with the hot water control turned up to max, and so a d7 of 50 I then ran the hot water and it was warmer, with d40 rising to reach 50 degrees. I thought I had tried turning the control to max before but I obviously was not patient enough, and didnt know how to monitor what was happening.

This I think explains the behaviour of the boiler as with the central heating on the flow temperature rises to 65, and so when the hot water is demanded the primary circuit is at around 65 so the water comes out warmer, but then cools slowly.

So the problem now I think is that the maximum setting on the hot water system is only 50. Is there a way that I can increase this?
I know the boiler can do it as two weeks ago it was providing piping hot water!

Thanks for any advice you can give me!
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It sounds like it's either doin warmstart,do u have the tap symbol shown on display or just the letter c flashing or u have snapped the hot water knob an the spindle is not turn in the pot on the pcb
Over the weekend I have been looking into the problem more. I can get the hot water to come out at a decent temperature when the heating is on by changing the settings for D73 (Warmstart offset Temperature), which makes it possible to change the setting D7 (warmstart temperature) to a higher value.

However, when the heating is off, the hot water does not work, the status code switches to S14 (hotwater operation), but the boiler does not provide enough heat to maintain the primary circuit temperature from the warm start setting, and so the temperature of the water starts off warm and then drops off untill cold.

Any ideas?
With the boiler completely cold, can you measure the resistance of each sensor ( with the plug disconnected ).

You have not mentioned the hot water flow rate. Lets consider the normal flow rate of 9 litres per minute.

Can you set the flow rate to half of that, namely 4.5 li/min, and tell us the relevant temperatures?

Trying to resurrect the old thread, hopefully somebody will respond - I'm having a similar problem and the last comments on this thread may be relevant in my case. Background, a couple of days ago my Vaillant Turbomax plus 828E got locked out with f29 error which subsequently changed to f28, got the boiler guy to fix it - turns out the PCB needed changing as he ruled out the other possible causes. PCB was replaced and boiler came back to life but the hot water temperature is barely luke warm, central heating is working fine. Prior to the lockout the hot water used to get really hot and we had to be careful when opening the hot water tap but now even with the hot water control dial turned to maximum, the water just doesn't get hot. 'The 831 Bunny' asked if the PCB had been changed and 'Bunnyman' seemed to know why he was asking that - just wondering if they were onto something that could help my problem ?
Yes get ur engineer back an get him to sort the jumper out on the pcb, they come preset fot sit valves if urs is a bit older it will hVe a honeywell valve, the jumper needs moving, hopefully hes kept the old pcb as he will need the jumper link off it
Thanks for the quick response - he didn't keep the old PCB. Boiler is around 10 years old. Are jumpers available separately and will he know which jumper to move without having the old PCB ? Boiler guy is very busy at the moment is this something that can be done on a DIY basis ?
No its not a diy, u will need the jumper, all new pcbs come without it asaik, u need to take off the old pcb,
Thanks, appreciate your input. I'll contact my boiler guy, hopefully he'll know what to do.

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