Vaillant Turbomax plus - F24 lockout

[dadgel]

Hi all,

I have a Turbomax plus 824E (or 242/2). Been having a problem the last couple of days with it locking out with code F24. Reset and all is fine, for a while, but it's doing it a couple of times a day.

Servicing manual suggests this code is due to pump failure, low flow, air lock etc.

Pump sounds/feels like it's running, and CH is working. Have bled pump using screw on front. Auto vent is open above pump. Not convinced it's either airlock or pump (but would appreciate any guidance on how to test pump further).

Some history:
Couple of years ago DHW not very hot. DHW clogged with iron oxide. Cleaned out, pipes flushed and magnaclean added.

Since then had similar problem with DHW, replaced plate to plate HEX and that improved matters. (Not convinced water is still that hot - but cold feed feels sub zero at the moment, and it is now good enough for a comfortable shower again.) Also replace PRV at same time as pressure had been slowly dropping and PRV was dripping.

Given the history of sludge and secondary hex blockage, I'm concerned that the problem might be with blockage of the primary heat exchanger. Is this likely, and if so is it possible to clean with water/acid/lemon juice etc? The price of a new primary heat exchanger gave me a bit of a shock...

And if not, how could I test to narrow down problem further?

Cheers for any assistance.

 

[turbomaxed]

think the Vailant service site had something the other day cant remeber codes sorry

Something like dont worry fault caused by cold weather or may have been dreaming it was late

 

[Agile]

I agree that based on the history further sludging is likely.

But to correctly diagnose the exact cause would be much easied for an expert at the boiler.

It is possible to clean the primary HE but that is not done by many engineers as its messy. I will do it but most will try to get you to agree to a new boiler!

Tony

 

[dadgel]

Thanks for the replies.

Fortunately this hasn't happened since. However hot water is still a bit tepid.

The gas modulator also seems to cycle quite rapidly - with the burner on full for only about 5 or 6 seconds at a time. I'm pretty sure that this is all cause by the sludge in the HE causing slow flow and the temperature to rise quickly.

Is a new primary HE not a cheaper option than a new boiler?

 

[Agile]

New primary HE is probably about £150 and takes about an hour to change. Way cheaper than a new boiler.

I clean them for about £180 inclusive.

But your symptoms still sound like a blocked plate or perhaps a blocked pump impeller!

To diagnose that measure the temps of flow and return in DHW mode ( see d40 and d41 on the display. Should be about 15 C differential if not blocked and if pump flow OK.

Inspect pump impeller be removing pump head.

Tony

 

[dadgel]

Thanks again for the response Tony.

DHW near useless now. Very cool unless the flow is super low.

Pump impeller moving OK. Drained down boiler and removed, checked and cleaned pump. Is working, spins ok, no blockage, refitted.

Whilst drained, I removed primary HE. This was in a pretty bad way - took it out to the garage and could hardly pass water through it at first. Gave a good clean with citric acid, can now pass water through it at a reasonable rate.

Also checked the "connecting tubes" - the one on the outlet of the HE had a blockage where the NTC sensor is. Guess a few flakes got caught on the sensor and this started to build. Cleaned that up.

So feeling quite chipper about getting the gunk out. However now I can't get the connecting tubes to seal to the HE. Have cleaned the surfaces on both, silicone grease on packing rings etc, but every time I pressurise it leaks.

Probably new packing rings will fix it - but anyone got any ideas that might allow me to get this working tonight?