Alpha SY24 fault diagnosis

[Dennis]

First, Hi all. Newbie here!

I have an eight year old Alpha SY24 system boiler that powers my house and an annex on two feed and return loops, both controlled by a seperate programmer. Until recently this system worked like a dream.
We then started to encounter problems which were diagnosed to a faulty water pressure sensor, which was replaced about two months ago. Since then, the system has degraded until virtually no heat or hot water.
After some elimination it looked like the pump, so telephone for the cavalry.
Cavalry arrives, hour or so later diagnoses pump problem, will return the next day to replace.
Next day, as promised, pump replaced with a similar, but not identical one. No change to system. New diagnosis - auto air vent blocked by sludge, pump maybe cavitating.
Next day, replacement air vent fitted, no change to system. New diagnosis: heat exchanger blocked by sludge.
Two days later, heat exchanger removed, cleaned and replaced. System now 'OK' but may take 'two or three days to get up to heat' [wtf?]. This comment was apparently based on my remark that [when the system was degrading rapidly] after a drain and refill it could take that long for the last radiator, very prone to airlocks, to clear and heat.
So, final diagnosis. The system is now working but needs a sludge clean and a magnaclean installed for which a quote is being prepared.
I do not disagree with anything in this comment, except the 'system working Ok' bit...
We have no heat. No hot water and the boiler repeatedly indicates a pump fault.

Sorry for such a long post, and I am sure that I have missed lots, but does this sound familiar to any of you guys? Any thoughts?
It's cold and I stink, as do the rest of my family...

(not really true, it's only me...)

 

[fireblade]

witch led is pump fault a or b

 

[Dennis]

Red continuous on top led
Flashing bottom led

Manual says: Pump fault. Really helpful.

 

[fireblade]

Looking at the schematic diagram the only thing that would tell the boiler the pump is not running would be too fast a temprature rise on the flow so barring an air lock on sytem check valves under boiler to make sure sombody hasn,t left one turned off blockage of some sort or faulty temp sensor or high limit stat

try and link the primary pressure switch

 

[Dennis]

Thanks for your reply.

'sludge' is now being mentioned, often, as a cause.

While I am not saying that the engineer is wrong, the fact remains that the system was flushed with mains pressure. Mains pressure was put in on the return and let out from the flow to ensure no airlocks in either the main flow and return or individual rads - worked backed from the last in the lines. The balancing pressure (i.e the pressure registered that remained constant) was 2.5 bar. Our mains pressure is 3.5 bar.
Correct me if I am wrong, but this indicates that the system is quite happy to push water at 2.5 bar around - coincidentally this is also the working pressure of the system.

I am prepared to accept the 'sludge' reason for the main CH system, it's many,many metres long.
What I am struggling to understand is why the hot water system is also not working. This is a DHW system, 3 feet from the boiler, so the total pipe run is less than 10 feet - that is also not working...

 

[fireblade]

Dennis the pump you said is not the same is it spinning free and correct rotation looking at the book it would rotate clockwise earlier in the book it says b flashing temp sensor fault whitch would hold off the burner does burner run for a few minutes

 

[Dennis]

I like your question.

Yes, the pump is spinning free.

We have maybe 50 secs of burn then shutdown.

Sorry, forgot to mention : top led is constant red

 

[fireblade]

It must be a hell of a blockage i would like to see this fault bit hard to tell on a computer just one last question your zone valve on the cylinder is open either two port or three port

 

[Dennis]

Not quite sure of this question.

Rather than answer this directly and confuse matters, I'll try and explain the system as a whole.

From the boiler,
feed & return to a DHW cylinder.

From the boiler,
feed & return to the CH system:

feed then encounters two three way valves, these are open if heat is requested, closed if not.

To take it back to basics, I have two f & r loops, with two programmers, but using one boiler.

Don't forget that this has worked perfectly until now....

 

[fireblade]

On the three port valves lock the handles over in manual and see if you get any flow through the boiler