heatline c24 overheat lockout only with HW.

[rjplumbing]

Heat line c24.

I run the hot water and the overheat symbol flashes after a few minutes.
Boiler works fine in heating.
I've replaced high limit and overheat stats and taken out the plate heat exchanger flush through with sludge remover which removed some black deposits, but the boiler still overheats. Has anyone got any ideas? Thanks Richard

 

[Slugbabydotcom]

HW sensor

 

[rjplumbing]

Thanks. I spoke to vailant as heatline are no longer around and I mentioned that and i was told it's unlikely. I don't think there really interested and they just phob you off.

 

[Slugbabydotcom]

IIRC these are just a heatline vizo. Notorious for the HW sensor and knowing these for the low outlay cost more of a service item than the start of a parts changing operation. You will find that Vokera part number 8484 is exactly the same part but much cheaper.

Next thing to be checking is the circulation and the next most notorious item is the diverter valve. It often sticks and sometimes leaks onto the motor head causing it to burn out or kill fuses at least.
Although in the line of fire for a circulation problem the pump is a natural suspect but these have always outlived the DV in my experience. Still needs checking though.

After that we are looking at fan / combustion stuff for which you would need to join the combustion chamber. We're not allowed to give any info to those who are not proven to be gas safe registered in the public forum.

Demir Dokum were incorporated into Glow worm /Vaillant a few years ago now. Demir Dokum/ Heatline boilers now have a Glow worm badge ie. the Vizo is a Betacom c and the Monza is a betacom 2

When I ask for parts I find that asking for them as a glow worm part often gets me a better price. Although they do change the casing and display design to try and confuse us. It's just a case of checking the manuals to make sure you're looking at the same set up.

 

[naanbread]

its very unlikely to be the HW sensor as previously stated, this is just an NTC thermistor on these if i remember correctly and its measuring the outlet temperature from the P2P h/ex. The Overheat stat is on the primary circuit so they arent linked as such.

another point raised is checking the fan and combustion area? not sure why this would be the case as it appears its working in heating. The primary circuit and most components work in the same way for heating and hot water so again, this wont be the issue.

Divertor would not cause for it to overheat, it would just lose the temperature down the heating leg and you would get no hot water at all.

It is most likely a restriction/blockage in the P2P, the most relevant test to carry out would be a simple temperature test based on the principles of heat flow.
Measure the temperature difference between the primary flow and return within the appliance before it goes into the plate to plate. Ideally the difference should be around 15-20 degrees. The hot water outlet temperature should be +/-5 degrees of the return temperature if you have good heat transfer. If you find that you have a very hot flow and return, but not much coming out of the P2P, and the heating flow isnt getting hot (diverter) then its not transfering the heat through the P2P and its probably blocked.

Changing parts is an expensive way of fault finding. The cheapest way to fix any boiler is to diagnose correctly what part is required. It doesnt matter how cheap a thermistor is, if you dont need it, dont change it.

I hope this helps,

NB

 

[nipper39]

First id check if he was gas safe before encouraging any one to play about in a boiler.

 

[rjplumbing]

I have replaced the secondary heat exchanger as well as the hw thermistor, which seemed to have solved the problem, unfortunately I have just found out that the boiler has some how overheated without using the hot water or heating, which I find hard to believe. Would I be wrong to think the pcb could be causing the issue. I am gas safe registered. I also agree with the comment about chucking parts at it, but I have tried to find out as much as possible before replacing parts, cheap or not. Has anyone got any ideas, much appreciated. Thanks Richard

 

[Agile]

Even if you were gas safe registered we cannot give advice on gas/combustion issues on this forum.

You should register for the Combustion Chamber section of the site.

But the advice from Piers is probably as good as you will get. ( At least if you add in checking the pump impeller ).

As he says a thermal survey is required to identify the problem quickly.

Tony

 

[Piers1989]

I have replaced the secondary heat exchanger as well as the hw thermistor, which seemed to have solved the problem, unfortunately I have just found out that the boiler has some how overheated without using the hot water or heating, which I find hard to believe. Would I be wrong to think the pcb could be causing the issue. I am gas safe registered. I also agree with the comment about chucking parts at it, but I have tried to find out as much as possible before replacing parts, cheap or not. Has anyone got any ideas, much appreciated. Thanks Richard

It's very unusual for the overheat stat to trip from cold. It's just a metalic strip that reacts to certain temperatures and breaks the circuit through it. So in answer to your question about the PCB it wouldn't be the issue, unless you are getting a good circuit through the harness and the overheat stat but still get an overheat fault displayed. Check for continuity through the stay and the harness and see if there is a circuit. It's possibly the overheat stat that has failed but an unusual issue for one to trip when the boiler is not on operation.

Piers

p.s Sorry for the spelling mistakes! i used my phone to type this (autocorrect)

 

[rjplumbing]

I have modulated the boiler down via the pcb to its minimum output setting to try and stop the boiler overheating. I checked the CH sensor and it seems to have the correct resistances, but now when I've checked the temp on the overheat stat pipe its reading about 95°c which is way above what it should be and the boiler wasn't locking out nor when I turned the room stst down did the pump over run and far as I'm aware it should run until the boiler ch temp hits 65°c. The tenants said it had locked out once before I got there. Anywone got any ideas. Thanks Richard [/b]