Alpha 28 Central Heating comes on for no reason!

[coopersim]

I recently had a problem with the heating coming on with the hot water - I've fixed this by replacing the diaphram in the diverter - that problem now sorted, so I thought!

Now the central heating timer is on for 1 hour in the evening, when I woke up this morning the heating was on full blast even though the timer isn't set to be on, thinking it might be the problem with the hot water again, but there was no demand from DHW.......

Any ideas peeps?

Much appreciated!

 

[Paul Barker]

Reading between the lines you have a CB28 and not the more recent CD28.

This is a very unusual scenario on a cb 28. on most boilers the culprit would be a thermister, but I never had this fault with an Alpha. The white thermisters were bullet proof, but if you have any other colour you need new white ones.

Or you might have an external problem.

A competent person would remove external controls from the equation, if it still does it he would be thinking on the following lines

1/ As it is a combi is the dhw flow switch stuck in the on position (absuletely unheard of on the cb28 but a possibility on the cd28 which uses the type of flow sensor which can fail in this way although it is extremely rare on an alpha very common on a biasi (for example).

2/ Some combi boilers behave this way with a dripping tap. but not an Alpha

If 1 or 2 then the return pipe (instead of the flow) gets red hot and the radiators don't.

3/ thermister is misinforming the pcb into thinking that the boiler is frozen so frost protection kicks in. White thermisters have been used for 4 years or so they are absolutely bullet proof. The only times I ever changed white ones I was wrong it was something else.

4/ pcb itself, but if that is your fault you will be able to knock me down with a feather.

 

[Paul Barker]

Oh there is sometyhing else.

If you have an Easystat likely you don't understand it.

This is why I said we would eliminate external controls by pulling out leeds inside the boiler so that we are dealing only with the boiler and nothing else.

Easystats should be scrapped for flaunting the trades descriptions act.nobody seems to understand them, But then that goes for the majority of programmable thermostats.

In wreckless following of government's unrealistic demands manufacturers of controls have produced a whole load of cack that anyone not a member of mensa with 20 20 vision and fingers devoid of arthritis hasn't a hope in hell of utilising so all everyone does is leave it on the whole time or off, if they can even work that much out.

But I suppose what they did with Northern Rock was a bigger crime.

 

[Agile]

Paul, isn't this the one with the mechanical diverter valve with the clip on switch which is faulty and on when it should be off?

It might instead be the diverter manifold section is not returning and thus holding the DHW switch in the on position.

This gives a demand for hot water and heats the rads instead.

Its easy enough for me to confirm which but a DIyer might more conveniently change the switch first.

Tony

 

[Gas2Air]

It does sound like the Cd28 range that has the mechanical motor that clips onto valve, easy way to test is unplug the 3 wire plug that goes to it when fault appears.

 

[Agile]

It does sound like the Cd28 range that has the mechanical motor that clips onto valve, easy way to test is unplug the 3 wire plug that goes to it when fault appears.

It does not sound like it to me because he said that he has replaced the diaphragm in the diverter valve!

Tony

 

[Gas2Air]

It does sound like the Cd28 range that has the mechanical motor that clips onto valve, easy way to test is unplug the 3 wire plug that goes to it when fault appears.

It does not sound like it to me because he said that he has replaced the diaphragm in the diverter valve!

Tony

Your very volatile tonight Tony. Is it because M&S sales fell by 6% in the last year?

 

[Paul Barker]

Yes Tony it is the cb28 as it has a diaphragm.

He might have not clipped it home properly or be unaware he has disturbed it's position, thanks for the nudge.

I never went to one which had failed in the position which would fire the boiler. Their usual failure mode (and a very common failure from this inadequate yet expensive part) is initially intermittent inability to sense flow leeding to total failure eventually. To test them properly you have to fire the boiler 50 times if it fails to register once out of 50 it's a dud.

If I owned an alpha of that generation I would put my own ball bearing lift up to alert a reed switch style flow sensor on the dhw pipework like found up on the left hand side of one of the glowworm combis, can't remember the model name right now.

 

[coopersim]

Can I just confirm that this could possibly be the DHW flow switch on the diverter that could be at fault?

Today it has vented water from the PRV due to it running so hot!

Thanks

 

[Agile]

Can I just confirm that this could possibly be the DHW flow switch on the diverter that could be at fault?

Thanks

Yes, I think thats what the thinking people might be saying!

Check its fully pushed down into position. If you have the skill measure its operation with a test meter.

Tony

 

[coopersim]

Just checking as there seemed to be some off topic ranting about dropping sales at M&S, and those bloody awful electronic room stats that everyone seems to hate!

Thanks all for your help as usual )