Can a faulty diverter valve cause random firing of boiler?

[Masood]

Afternoon all,

Went to look at am EcoTEC Plus 831 today, customer complaining that rads get hot when DHW is run. Lo and behold, the flow pipe gets roasting hot when tap is opened, so I'm thinking diverter valve. Apparently BG changed this just over a year ago.

Then she tells me that the rads sometimes get hot at random times with no call for heat, or DHW. I checked whether warm-start is switched on, and it's definitely not. Could the diverter be causing random firing? I can't see how it would, but I'm happy to be corrected!

Also, I know on some boilers when the NTC stats are faulty, they kick the frost protection in at higher temps than they should. Anybody know if this happens on these boilers?

Cheers!

 

[lame plumber]

never trust a custard, but sounds like jammed diverter valve.

 

[Masood]

never trust a custard, but sounds like jammed diverter valve.

That would explain the rads heating when DHW demand is on, but how would that cause random boiler firing? Not saying I disagree, I just would like to understand the process by which that could happen..

Cheers!

 

[ambrosia]

a diverter valve should last longer than a year, something doesnt smell right,
i'd ask the customer when the problem started and after the new diverter valve was put in did it work for awhile or did it not fix it at all

 

[jtsplumbing]

Get her to check dates if less than 1 year get BG back.

 

[Masood]

a diverter valve should last longer than a year, something doesnt smell right,
i'd ask the customer when the problem started and after the new diverter valve was put in did it work for awhile or did it not fix it at all

Get her to check dates if less than 1 year get BG back.

Thanks guys. Whatever the BG guy did apparently didn't help at all, and it's definitely over a year.

But really, I know that the DV is faulty, what I'd like to understand is whether that can cause the boiler to fire randomly, and if so, how? This is purely to increase my own knowledge, as I can't see how, even if the DV is jammed open, any water could flow past either flow switch and trigger the burner, as there is no demand.

If this is not possible, then could faulty NTC stats be triggering frost protection at much higher temps than designed, the way they do on other makes?

Oh, and final question - is it possible to strip down and service these DVs? The merchant says they don't do a service kit like they do for other boilers, but a new DV is pricey and she doesn't have a lot of money...

 

[Billy Bob Bob]

it sounds like the dv or dhw flowswitch if it has one fitted got a mi,s on it you can post up not familer with this boiler

 

[ambrosia]

a customer who wont pay and a difficult time consuming problem to fix. not a good combination

 

[Nostrum]

Why isn't British gas still involved?

 

[Masood]

a customer who wont pay and a difficult time consuming problem to fix. not a good combination

Not a case of won't pay, she has always offered to pay, never quibbled over anything. I just know she hasn't got a lot, and for reasons I won't bore you with, I want to help her out..

Why isn't British gas still involved?

Because she has lost faith in them. Also, as it's over a year, it's out of warranty...

 

[Masood]

it sounds like the dv or dhw flowswitch if it has one fitted got a mi,s on it you can post up not familer with this boiler

Oooh - flowswitch! Hadn't thought of that. It's one of the turbine type jobbies, but could be sending a spurious signal perhaps?

Installation & servicing manual here:

http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf

Thanks! 🙂

 

[TBServices]

Does the turbine sensor have a light on these?

Certainly sounds like the DV valve though, problem with customers is getting the truth out of them.

 

[Masood]

Does the turbine sensor have a light on these?

Sadly, no.

Certainly sounds like the DV valve though, problem with customers is getting the truth out of them.

Agree, I'm just struggling to visualise how it could cause the boiler to fire. If no taps are open, and the pump isn't running, how can any flow occur through the DV. Maybe it is just a case of swap it and see, but I'm really reluctant to do that...

 

[Billy Bob Bob]

what does the aqua sensor do? bet its a dhw flowswitch if it is i bet its sticking

 

[R1CKY]

The tap symbol should light up on these when the flow switch/aqua sensor is activated. Not suffering from backflow when a cold tap is being run? I know on certain boilers it will fire on DHW mode because of this.

Pre-heat is definitely turned off? That was my first thought. You have to fiddle with the DHW stat to de-activate it.

 

[Masood]

Pre-heat is definitely turned off? That was my first thought. You have to fiddle with the DHW stat to de-activate it.

Definitely - first thing I checked - as you say, that would cause all the symptoms described..

 

[vern]

Does the turbine sensor have a light on these?
.

No Tom that's Ideals

 

[vern]

Whats controlling the heating, maybe a duff prog stat?

 

[gas frank]

Aquasensor

Select D22 and press the i button, open a hot water tap.

• 1 = flow detected
• 0 = no flow detected

Voltage checks can be done as follows

• Across red and green wires with no demand = 0vdc or 5 vdc ( depending on hall sensor position ).
• Across red and green wires with demand = average 2.5 vdc proves flow has been recognised. ( can also use terminal 9 as dc neutral )

 

[abc_plumb]

Check the voltage is sent by the pcb to the DV motor.
Ive replaced a few boards with this kind of fault.

 

[gas frank]

D 35 position of diverter valve. Select i button

0 = heating ( normal )
1 = hot water
2 = centre position

Resistance = 170/180 ohms approx ( outside pins )

 

[abc_plumb]

There is a quick surge of 10-15dc volts when the boiler starts to the DV motor.
If this is not present it's a board issue. What's strange about it that everything else works fine. The why to test it is, switch off the boiler place the multimeter probs on the 2 wires on the board, get another person to switch the boiler on.