Vaillant Turbomax 828 - F24

[ClockPie]

Hi. We have the Vaillant Turbomax 828 combi boilder, been here since we moved in 6 years ago. (edit: 2001 install! )

Randomly, maybe once or twice a year it locks out and turning it off and on again fixes it. Usually when its *very* cold outside and the incoming water is cold.

Anyway, over last week days we've had 3+ F.24 lockouts which is more than normal. The heating was on 5-6pm then I got in the bath at 7pm and boiler was locked out. Resetting again and fine, but the hot water was very variable in temperature which I've never noticed before. (Flow was good and normal, and its a simple direct tap). After bath, wife ran more hot water, and she said the temperature varied - but I was watching the LCD and the temperature didn't fluctuate much. (edit: LCD was 65-70' - whereas HW temp is set at 42' - so that's quite a difference.... If boiler was keeping water at 65-70 and actual water was fluctuating between (guess) 20-40 - suggests Water-to-water HE blocked?)

Pressure is 1bar - and that's what it was on when we moved in so we've kept it at that.

The original pump failed a year or so ago and we replaced that, and I think pump is fine as heating works well. We have combi-mate and a magnetic trap which we clean out.

I have searched, and suggestions seem to be air-pressure switch or heat exchanger. (Is the heat exchanger the water-to-water sardine can one? Or the flame-to-water? Assume its water-to-water).

Other suggestions I've ruled out seem to be the diverter valve, but the CH pipes do not get warm unless heating is on. Pump (heating is fine when its on) Also no water in boiler, though there is. Or NTC sensors but I'm sure if that was the case the issue would be more constant.

I hear pressure should be 1.5bar when cold - is that correct? Not going to find any weak heating plumbing if I put it up am I

I've not checked the pressure-vessel but water pressure doesn't rapidly rise when hot, so assume that's OK. (What should it be? I'll check next time I drain the boiler)

From my symptoms above, which seem slightly different to other posts, any other suggestions?

(Thinking of replacing DHW HE first; failing that air pressure switch (though no idea what that does!); failing that Primary HE)

Thanks


Edit: I'm sure its an 828 as that is said on the installation paperwork. Manual says the DHW HE is PN 065088 - but elsewhere PN 065153 is mentioned? (different number of plates? ) Assume the manual is the PN to use?

 

[nickjb]

When our vaillant started fluctuating on temperature it was the flow sensor. There's a little black cylinder with an impeller in it. Ours gummed up so the water was flowing but it span intermittently. I opened it up (just a circlip on the front) and cleaned it out. That was maybe 5 years ago and its been fine since. A very pleasing easy fix. Don't know if this relates to any of the other symptoms but its easy to check and you may have multiple faults. Obviously turn the water off first.

 

[ClockPie]

When our vaillant started fluctuating on temperature it was the flow sensor. There's a little black cylinder with an impeller in it. Ours gummed up so the water was flowing but it span intermittently. I opened it up (just a circlip on the front) and cleaned it out. That was maybe 5 years ago and its been fine since. A very pleasing easy fix. Don't know if this relates to any of the other symptoms but its easy to check and you may have multiple faults. Obviously turn the water off first.

Thanks. I hadn't considered the flow sensor - though in the manual its called an Aqua Sensor and my brain just thought it was a senor to detect the presence of water, not the flow. Looking at the functional pictures, this is only on the hot water circuit? Guess its used to detect when a tap is open? It deffo does that alright, but if its variable speed back to the PCB then I guess if there is debris there then it could induce random symptons. So nice idea. And you reckon the clean is easy? That's the fresh water side, so should't have boiler gunk in it - but who knows what has come in on the water main. (And guess any gunk on the fresh would've got to the DHW HE too.

Appreciate the time taken to reply

 

[nickjb]

Yes it just spins when water is flowing, ie a tap is open, to tell the boiler to heat it. Only on the hot water, not the heating. Very simple job to check and clean. The cover is just held in with a circlip and the impeller floats in the chamber so just pulls out. Just turn off the water and drain the hot by opening a couple of taps. Mine is also an 828 and there was noticeable gunk in there. Its quite a dainty part so wouldn't take much to mess it up but its been fine e since the clean

 

[ClockPie]

Yes it just spins when water is flowing, ie a tap is open, to tell the boiler to heat it. Only on the hot water, not the heating. Very simple job to check and clean. The cover is just held in with a circlip and the impeller floats in the chamber so just pulls out. Just turn off the water and drain the hot by opening a couple of taps. Mine is also an 828 and there was noticeable gunk in there. Its quite a dainty part so wouldn't take much to mess it up but its been fine e since the clean

Cool. Not even a boiler drain down then if its fresh/hot side....
Could easily be that so long as the sensor is "variable" not just flowing/not flowing.
Will try after the weekend.

 

[ReganAndCarter]

There are three LEDs under the LCD display. The right one flashes when the hot tap is open to show hot water demand. Middle one shows when the burner is lit. If the right one doesn't keep flashing at regular intervals with hot tap open, it could indicate a sticky aqua sensor. If the middle LED goes on and off, it may mean that your dhw plate heat exchanger is blocked with rust particles on its heating side.

Hot water going hot>cold>hot is more often plate heat ex blocked up. They can be cleaned out with something like Spirit Of Salts. Cheaper than buying a new one.

Don't worry about it being old, these boilers came from a time when Vaillant made proper boilers. They're durable, reliable and simple to fix. Parts are plentiful and not bad value. If it wasn't quality, it wouldn't still be working after 17 years.

 

[ClockPie]

There are three LEDs under the LCD display. The right one flashes when the hot tap is open to show hot water demand. Middle one shows when the burner is lit. If the right one doesn't keep flashing at regular intervals with hot tap open, it could indicate a sticky aqua sensor. If the middle LED goes on and off, it may mean that your dhw plate heat exchanger is blocked with rust particles on its heating side.

Hot water going hot>cold>hot is more often plate heat ex blocked up. They can be cleaned out with something like Spirit Of Salts. Cheaper than buying a new one.

Don't worry about it being old, these boilers came from a time when Vaillant made proper boilers. They're durable, reliable and simple to fix. Parts are plentiful and not bad value. If it wasn't quality, it wouldn't still be working after 17 years.

Thanks for taking time to reply. Yes, same thing when backpacking - the older dangerous busses/planes are the ones to use as they haven't crashed (yet!)

The LEDs are all behaving as expected. In the example where the hot water temp varies, the green LED is flashing (non stop) and the middle yellow is lit. (Though you can hear the flames cutting in and out as needed) and the LCD temp varied between, say, 65-70'. And the hot water was 20-40'. so from looking at the LEDs/LCD everything looked normal.

By "plate head ex" do you mean the main heat exchanger (flame-to-water)? Happy to clean that - never heard of Spirit-of-salts, will google/purchase and clean anyway. Do you think the DHW HE is worth changing (c. £45) at the same time? (edit: aha - strong liquid descaler (Kilrock?). Assume use neat? 3x500ml for £13 from Amazon? My local screwfix/toolstation don't appear to stock it)

And stupid question - the manual says the parts come out by removal of clamps. Does anything need to be done to reseal? new o'rings? or anything else?

Thanks

 

[ReganAndCarter]

Plate heat ex is the hot water 'sardine tin' heat exchanger, not the main one. F24 can be a number of things and may not be related to fluctuating hot water temp. With you symptoms, I think it would be better to get an experienced engineer to look at it. May save you time a aggravation in the long run.

 

[ClockPie]

Thanks for clarifying. Seems to be many names for each HE - so just being pedantic checking

OK, if its the sardine tin I'll replace it - yep cost more - but once done its done. "genuine" parts seem to be £40-50 on ebay.

No offence to anyone in the trade, but I've never had luck and found a plumber/gasman who I would want to work with Don't know what it is - but never been inspired with confidence that they are there to help me rather than fill their free hours with 25 trips to van for no reason. Electricians, plasterers, roofers, welders, molers have been absolutely fine - so I'm not anti-trade in the slightest. I'd love a contact who'd come and we could chat and go through things and get it fixed (and pay, obviously). (Of course, online most are really helpful where they can, but just none I know in the flesh lol)

However, I also love DIY And I like the challenge. I like asking questions, getting advice and learning, and like fixing things. I'm happy to learn and replace things, and if nothing fixes it - then (a) I've got a box of good spares; and (b) I know how to fix all the bits I've replaced. And then I'll play "plumber-roulette" again But for now, I'm happy to play.

So plan of attack:-
- replace DHW/plate HE with new
- check/clean aqua sensor
- check/clean pump if needed (as, according to manual it needs to come out to access the DHW HE) edit: Looking at the boiler, there seems no need for the pump to come off? Seems to be plenty of room to get at the HE and get it out without pump removal?
- Clean diverter valve (as, according to manual it needs to come out)
- Check/correct expansion vessel air pressure.

Whilst its apart I may clean the primary HE anyway, and check no birds have nested in the flu edit: No, don't think I will clean primary HE!

Can't be much else lol (!) - NTC sensors/PCB lying maybe. Not likely to be gas related due to the symptoms.

We'll see

edit: Ordered genuine parts, new DHW HE and new diverter valve, and washer kits etc £80 for both which isn't bad, and far cheaper than the laughable "list" price. I'll clean the old ones up and keep as spare as needed.

 

[ClockPie]

I hate incomplete threads where you never find out what happened.
Anyway, since the last post in April, the boiler has been 100% perfect - so I have stalled this.
Couple of days ago I replaced the shower quadrant frame (long story!) - and had our first shower in a week (had been bathing!) and the boiler cut out twice. Not related, just coincidence.

So today:-
Based on plan above:-
- DONE: replace DHW/plate HE with new
- DONE (was clean): check/clean aqua sensor
- DONE: (Pump doesn't need to come out to remove HE, only if you knock the pipe behind the pump and need to reseal!) check/clean pump if needed (as, according to manual it needs to come out to access the DHW HE) edit: Looking at the boiler, there seems no need for the pump to come off? Seems to be plenty of room to get at the HE and get it out without pump removal?
- DONE (Diverter valve clean, but replaced with new): Clean diverter valve (as, according to manual it needs to come out)
- (Not appearing to be an issue) Check/correct expansion vessel air pressure.

There was some black debris, looks like corrosion and/or HE eating itself. There is a mag-filter on the system which should be removing it, but clearly not all.

So will see how it goes