Keston C55 Strangeness

[Comedynose]

Greetings all, I'm looking for some advice and suggestions.

I've got a Keston C55, manufactured in 2006, which has been running the house central heating successfully for about seven or eight years.

I know that Kestons are at best a dark art and usually the boiler that everyone loves to hate, but this one has done ok so far.

The recent problem that has emerged is that the boiler fires but doesn't run for more than a few minutes, claiming it's up to temperature.

The display shows the operational mode and the flow temperature, and the sequence is thus:

1. Switch on demand for heat.
2. Boiler enters A mode as it takes some internal readings.
3. Boiler enters 1 mode and spins up the fan to full chat as it runs the preignition sequence.
4. Boiler enters 2 mode for ignition and sparks up with a nice woof.
5. Boiler enters 3 mode and starts heating water like a champ. The flow temperature rises from 13 up to about 19 in about five or ten seconds, then the fan throttles right back, seemingly to an idle mode. The water temperature creeps up ever so slowly and the flue doesn't get hot to the touch at all. It does this for about four or five minutes then...
6. Boiler enters 6 mode. Burner not running as the boiler is up to temperature.

Now, once thing I can't fault this boiler on is it's ability to throw wobblers spawning error codes. If the thermistors go short circuit it should report it. If the thermistors go open circuit it should report it. If the temperature differential is too high or too low, it should report it. If there's flue overheat it should report it. If there's an ignition problem, etc. etc. The diagnostics are really good.

What's troubling me is that there are no error codes at all.

The boiler runs CH only, with no DHW requirement. It runs off the top thermostat, which the boiler knows is set to 62. I've set the redundant stat to the same temperature as well, just in case.

It knows the flow temperature is 22. It seems rather like the boiler is behaving exactly as it should, apart from the fact that it's about forty degrees too cold! Why on earth does it think that it's up to temperature?

At the moment I'm just trying to understand the mechanisms at work. Can anyone shed any light on what part of the process might be going wrong, or has anyone encountered similar problems.

Thanks in advance.

 

[Agile]

So what have you done to check the operation of the pump?

Do you work with computers?

Tony

 

[Comedynose]

So what have you done to check the operation of the pump?

Not a whole hell of a lot. The systems uses an external pump that augments the internal boiler pump. The internal pump vibrates smoothly and warms up so I'm assuming the motor at least is working, but I've not done anything to check the efficiency.

Do you work with computers?

Ah damn. Is it that obvious?

Yep, IT technician, for my sins.

Thanks for your help, I do appreciate it.

Pete

 

[Dan Robinson]

Yep, IT technician, for my sins

Can spot them a mile away

 

[simond]

Well I don't know anything about Keston C55's - other than how to remove them from the wall and get them into a skip. We've done over 5 this year so far.

IT Professionals were, in my experience, the most likely user-choosers of Kestons because the blurb pushes their buttons.

But this isn't helping. Most boilers with modulating burners incorporate some software to monitor the flow and return temps, as this is what ultimately decides the fan speed/gas rate.

If the electronics detect a faster than intended/expected temperature rise they will throttle the boiler output down and see what happens.

So, your Keston issue will be either an obstruction to flow (this could be the strainer mentioned in the MIs that should be in your pipework) such as a seized pump, motorised valve etc, or some internal electronic fault or blockage.

In the first instance I would be checking the flow and return pipes from the boiler. The filter is a good bet (if its been fitted), especially if no-one has ever cleaned it.

I've attached a link to a picture below.



But the best place for a Keston is a skip, ask anyone else who's had one.

 

[simond]

Well I don't know anything about Keston C55's - other than how to remove them from the wall and get them into a skip. We've done over 5 this year so far.

IT Professionals were, in my experience, the most likely user-choosers of Kestons because the blurb pushes their buttons.

But this isn't helping. Most boilers with modulating burners incorporate some software to monitor the flow and return temps, as this is what ultimately decides the fan speed/gas rate.

If the electronics detect a faster than intended/expected temperature rise they will throttle the boiler output down and see what happens.

So, your Keston issue will be either an obstruction to flow (this could be the strainer mentioned in the MIs that should be in your pipework) such as a seized pump, motorised valve etc, or some internal electronic fault or blockage.

In the first instance I would be checking the flow and return pipes from the boiler. The filter is a good bet (if its been fitted), especially if no-one has ever cleaned it.

I've attached a link to a picture below.



But the best place for a Keston is a skip, ask anyone else who's had one.

 

[Comedynose]

IT Professionals were, in my experience, the most likely user-choosers of Kestons because the blurb pushes their buttons.

I plead non est mea culpa - I didn't choose the bloody thing!

But this isn't helping. Most boilers with modulating burners incorporate some software to monitor the flow and return temps, as this is what ultimately decides the fan speed/gas rate.

If the electronics detect a faster than intended/expected temperature rise they will throttle the boiler output down and see what happens.

OK, that makes sense, thank you.

So, your Keston issue will be either an obstruction to flow (this could be the strainer mentioned in the MIs that should be in your pipework) such as a seized pump, motorised valve etc, or some internal electronic fault or blockage.

In the first instance I would be checking the flow and return pipes from the boiler. The filter is a good bet (if its been fitted), especially if no-one has ever cleaned it.

Well, the plot is thickening a little bit. I mentioned in my initial post that we use it for CH only, leaving the DHW input and thermostat redundant. This afternoon I elected to try moving the switched input from SL1 to SL2, that's the DHW input instead of the CH input.

The boiler fired up and has maintained stable operation for an hour so far.

This maybe raises more questions than it answers, foremost of which are:

1. Does the boiler run a different, more nuanced, operational programme for heating CH than it does for DHW?

2. If it does, does this offer any helpful information for diagnostics?

3. And perhaps this is the most significant for me...can I just leave the input on DHW and run the CH with it? My simple thinking is that heating water is heating water irrespective of what it's for, but I'm ready to be told that that is hopelessly naive.

But the best place for a Keston is a skip, ask anyone else who's had one.

This is something that is becoming abundantly clear! I've read lots of the web this week and, frankly, none of it's good.

I'm sure this one will meet a skip before long, but channelling the Gladiatorial spirit "Not yet...not yet."

Thanks to everyone for your insights so far. I do appreciate it.

 

[Agile]

That's an odd thing to do but it seems to have worked.

I would say leave it there and just use it.

If I ever had the time then I would look up the MI and see what has gone wrong with your boiler.

Tony

 

[Comedynose]

Thanks Tony. As it looks like running in this configuration isn't dangerous or galactically stupid I'm just going to leave it there and see what it does.

Thanks everyone. Let's hope it keeps going.