Vaillant CH Problem

[matt666]

Hi all,

I have a Vaillant 828E which appears to be working ok under normal circumstances. However if you run the shower it sometimes turns the heating off. I understand a combi is supposed to do this, but mine doesn't turn the heating back on again! I've left it a couple of hours before and it doesn't come back on. If you run a hot tap until it gets warm then turn it off, the heating will kick back in and everything is fine again.

Just had the expansion vessel replaced which has fixed the pressure problem I was having, I was hoping it would also fix this problem too but it still does it. Any ideas?

Thanks

 

[hazetimesfive]

sticking divertor valve? dunno whats inside this boiler but probs something like that.

 

[matt666]

sticking divertor valve? dunno whats inside this boiler but probs something like that.

Hi,

That was my thought after doing some research, but would it explain why a blast on the hot tap turns the heating back on?

 

[Agile]

Thee are very simple rules to diagnose a sticking diverter valve in the FAQ on this site all ready for you to read1

 

[matt666]

Thanks, just read the faq and it certainly sounds like a sticking valve. Would using the hot tap cause it to unstick? If one time using the hot tap doesn't work, can you operate it manually?

 

[hazetimesfive]

no, it needs replacing before it fails completely.

 

[Agile]

As a temporary stopgap I remove the actuator and set the diverter valve in 75% DHW and 25% CH.

That gives pretty good operation on both until I can fit a new divertter valve.

Although I usually carry one for that model anyway!

Tony

 

[hazetimesfive]

couldnt that cause scalding at low flow rates?

 

[matt666]

Bit of an update as I think I've got a better idea of the symptoms -

Hot water always works fine

When the heating is playing up it shows a high temperature (around 70 degrees) on the display and displays a status of s0, which according to the manual means no heat demand, or as I understand it, it thinks the water is up to temperature and doesn't need heating. This is different to the s30 it shows when the wall thermostat is up to temp.

Over time the temperature drops a little to around 65 degrees, the boiler kicks in for a few seconds until it goes over 70 then stops. Pump overruns for a bit then back to s0.

While this is happening, the radiators are cold, so evidently the water isn't at 70 degrees.

There is a diagnostic function which tells me that the diverter valve is in the correct position, i.e. heating.

At the moment my old trick of using the hot tap is not making the heating come back on, so whatever it is looks like it's failed for good.

Not sure if this is related but over time the pressure is increasing with the heating being off which I'm lead to believe is either a pin hole in the heat exchanger, or the filling loop.

Anyone seen this on a Vaillant 828e before?

I've had a heating engineer out but as this was an intermittent problem which didn't happen when he was round, and he was relying on my explanation of the symptoms, we're a bit stumped.

Thanks

 

[Agile]

There is a diagnostic function which tells me that the diverter valve is in the correct position, i.e. heating.

Thanks

Unfortunately that function is only as good as the electronics and does not LOOK at the diverter valve.

It just shows when the diverter valve has been told to go!

But you can look at it yourself !

What you have described could indicate a PCB error but luckily I dont think that will be the case but it would be based on what you have said.

When left in that situation does the burner fire up again to keep it hot?

The 70 C is the temperature in the boiler and not the radiators!

Tony

 

[matt666]

Yes, while radiators are cold and heating on, boiler temp drops to around 65 degrees then fires up for a few seconds until it gets to 70 then stops. Rads still cold.

I guess if the diverter valve was stuck in hot water position, the water temp in the boiler would stay hot for ages as it's not being pumped around the rads - and when it did drop it would only take a few seconds to get back up to temp... so could explain that, and also why the s0 code. The water is actually hot enough, it's just not being pumped around the system to get cold again.

Think I need to get the heating engineer back to look at the valve!

 

[matt666]

In case anyone searches this problem and is interested in the solution, it was indeed the diverted valve. Replaced and it's all working fine now.

Thanks to Agile for his correct diagnosis.