Vaillant Turbomax 828E

23 Nov 2008
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United Kingdom
I have a Vaillant Turbomax 828E, 8 yrs old this month, has recently started playing up again. The problem is CH comes on by itself and wchich some how affects the not wate temp, which is not as hot as before.

I can hear this when this happens, as the pump comes on the CH pipes start rattling in my bedroom !!

I've checked the timer and and reset it so that no heating is required but problem still exists and is intermittant. I've turned the temp right down to stop this but not sure where to go next. Is this the timer (manual clock in this case) or the diverter valve etc.
any help will be appreciated.
thanks in advance
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It sounds like your diverter valve is sticking.

The reason the CH is coming on is the boiler trying to HW preheat. To disable this while you get the boiler repaired, turn the hw dial to 12 o'clock then all the way off, wait a couple of seconds and return the dial to its original setting.

2 points: when you turn the power off then on - can you hear the motor powering forward, then back and then shuffling in the middle? It should be a smooth sound. The other is to look at the holes on the side of the valve - if they are tiny 2mm ish, you have the old type and a new one is definitely recommended P/no 252457
thanks Beerlover

I've just powered it on and off and can hear the motor clicking forward and then back, its is a clicking noise and I wouldn't call it a smooth operation but I'm not an expert but the holes on the side of valve are 4mm dia (call me sad but I've just measured them!)

while I was doing this, Mrs tells me the rads have become hot again, not sue if the using HW triggers this.

Only two nuts on the valve, so if I can drain the system is there anything else to watch for when changing the valve.

Also does any one know how the light on the timer works in different modes, should it be off in night mode etc

cheers again,
The Diverter is very easy to change drain the boiler & unplug the motor first.Loosen nuts first to make sure the boiler is drained, if the boiler glugs water,this is a good time to repressurise the expansion vessel (at the top back of the boiler 10 psi or 0.7 bar.

Turn the HW preheat off as I explained but the rads will heated when you draw hot water till it's changed.

The night setting is off, day is on & clock is timed.
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Just an update for anyone who reads this, fitted the valve last weekend, problem solved, so far so good. Valve cost 90 pounds including vat and postage, fitting was no problem, 1/2 hour job, draining and refilling the system was the hardest part.

did ask a local plumber/gas engineer for a quote, he said 99 pounds + parts. valve cost from local plumbing store was 125+vat. this gave me the incentive to get off me butt and do it myself.

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