Alpha CB24 - Hot & Cold -= Run out of ideas ? now =-

[TimB2010]

Hi All,

We have an Alpha CB24, it has started to cut out when the hot it running, after 5-10secs it relights and this goes on and on over and over.

With just the heating on, it doesnt cut out at all.

Showers go hot and cold, and hot tap is dreafull!!

We have had the engineers out (Pay for insurance) and they said that it was a blocked/scaled heat exchanger which isnt covered.

So.. We had:
1) Radiators flushed with x400
2) New heat exchanger fitted.

Right away, this didnt change a thing, so we then:
3) changed both top and botton temp sensors..

And its still the same?

Has anyone else got any suggestions why it could be cutting out please?

 

[smuudge]

Hi, i have replaced both sensors, and PCB, due to various faults. (The CB24 isnt great for reliability sadly) The last problem was our hot water being tempramental, coming on and off when it felt like it and finally no hot water at all. The part to replace would be the diaphragm as this solved the problem isntantly, cant remember the part number but they are £21 from PTS. Takes maybe 1 hour to do if you know what you are doing. Hope that helps!

 

[Paul Barker]

Hi, i have replaced both sensors,

usually Alpha thurmisters are very reliable much more so than a host of other makes, and your probably didn't need changing, unless they were some very early red ones which should have been changed by a clued up service person for the newer white ones 4 years ago. Unless you don't have it serviced by someone clued up

.and PCB, due to various faults.

I have never had to change a CB pcb to fix a fault unless I dropped a screw on it while it was live or flooded it, one of the most reliable pcb's in the industry

(The CB24 isnt great for reliability sadly)

there is only one design fault, the horseshoe shaped domestic hot water flow switch, the diaphragm is no less reliable than any other boiler with differential pressure sensing.

The last problem was our hot water being tempramental, coming on and off when it felt like it and finally no hot water at all. The part to replace would be the diaphragm as this solved the problem isntantly,

and so all Alpha owners with dhw problems need a diaphragm? what a kute world it is in the kidergarden.

Takes maybe 1 hour to do if you know what you are doing.

and is never achieved if you don't. Not an easy job as boiler parts changing in the industry goes, but 1/2 as difficult as a Worcester Cdi. But neither should be tackled by a novice who doesn't like water pouring out from the boiler after they have finished.

 

[Paul Barker]

Has anyone else got any suggestions why it could be cutting out please?

Without being there it is very hard to say. The blocked calorifier is favourite.

did it fix the problem for a while? or did it make no difference right from the get go? might be blocked again.

Shut off the valve on the cold water supply just beneath the boiler. Go to a sink basin or bath with seperate hot tap. open that hot tap, does water should not flow, if it does you have a mono tap or shower which is blending hot and cold, go round the house listening to all mono and shower's to listen for water flowing. Deal with the culprit.

Other than that as in my previous post dhw flow switch is poorest on in industry I would be checking that, without being there not much more I can say. But if I was there it would be fixable.

Unlikely to be diaphragm since once it has failed to hold pushrod across it doesn't reattempt until the water flow has seased and restarted. but you are saying that the boiler repeats it's cycles.

Everything you have said points to the insurance fitters diagnosis but being on scene is the only real way to be sure.

When having a powerflush always get a guarantee, and have a filter fitted at the same time. Only an opinion. Obviously this costs more money. but money spent on a flush which doesn't fix the problem is more expensive than more money spent on a flush which does.

 

[TimB2010]

Thanks for taking the time to anwer

did it fix the problem for a while? or did it make no difference right from the get go? might be blocked again.

I think that it is getting too hot, would it be dangerous to unplug the lower sensor and plug it into one of the old sensors that is removed and see if that stops the cutting out?

Right after the pressure was back up and the boiler started, it went back to 5-10sec on the hot tap, and 25-30sec on the tower before it cuts out. after 5secs it relights and does this over and over. If it was sludge i would have thought it would have got beter for a while before blocking again?
There was no debris in the old heat exchanger and we also chemically cleaned the old one a few times and that made 0% difference

Shut off the valve on the cold water supply just beneath the boiler. Go to a sink basin or bath with seperate hot tap. open that hot tap, does water should not flow, if it does you have a mono tap or shower which is blending hot and cold, go round the house listening to all mono and shower's to listen for water flowing. Deal with the culprit.

Will do that today

But if I was there it would be fixable.
Are you local to worcestershire?

 

[TimB2010]

Shut off the valve on the cold water supply just beneath the boiler. Go to a sink basin or bath with seperate hot tap. open that hot tap, does water should not flow

I have turned the stop on the water 90 degrees to cut it off. When i now run the hot water tap on the sink, it flows with cold water just as much as the cold tap !!

is this wrong? should no water come out untill the cold stop tap is turned back on?
When the stop back on, the bioler then fires up.

Could i (you) have found the 5 month problem !!
Only the shower makes a very small his and the other mixer tap silent.

 

[TimB2010]

UPDATE:
I have unplugged the lower sensor and plugged it into a spare sensor off the boiler.. The combi still cuts out and restarts exactly as before.
So i guess i have illiminated the combi overheating?

Secondly, can someone please confirm that when the cold feed to the boiler is turned off, then no water should come out of the hot tap? is this the case for all combi`s? any exeptions?

With ours turned off the water flows from the hot tap as fast as the cold!!!
Plumbing error?
faulty mixer/shower?
I cant hear any gushing over the mixer taps.

 

[TimB2010]

UPDATE2:

Ive just ripped the side off the bath and managed to get to the 2 pipes leading to the shower.

When the hot tap is running, the cold pipe to the show gets colder, and the hot pipe also gets cold.

This HAS TO mean that the shower is leaking cold water to the hot?

Would love if someone would confirm as tomorrow im going to buy an isolation valve, cut the cold pipe and fit it in !!

 

[idealnumber1]

is it pipped up correctly???????
hot and cold pipes wrong way round.
ive had this boiler in my house since i moved in and never had a problem

 

[picasso]

your right the cold is passing into the hot , fit a non return valve to the hot and cold pipework to the shower, then try the hot tap with the hot water isolated from the boiler, there should be nothing coming from the tap.

 

[Paul Barker]

Yes sort this out first then see how combi behaves.

Not saying it is the only problem but it is a typical problem which has to be fixed before you can proceed.

Sadly the plumbers who fit mixer devices don't also repair boilers so have no idea of the mayhem they leave behind.

Like the driver who has never had an accident but seen plenty in their rear view mirror.

 

[TimB2010]

THANK YOU SO MUCH ! ! ! ! ! ! ! !

I fitted a stop valve on the shower cold feed and now we have constant hot water downstairs on the bath and the sink !!

Ive ripped out a wall tile and the shower mixer, so will be replacing it ASAP !

The boiler still cuts out, but after long periods of time. Is cutting out, a combi boilers normal methods of maintaining a set temperature?
Or does it create different temp water some other way?

Thinking about it, the engineers should have picked this up when they turned off the boiler cold feed, took off the heat exchanger and water still ****ed everywhere !!

Thanks again everyone, especially Paul

 

[TimB2010]

Well..... Looks like i spoke too soon !!!

We fitted a new shower mixer and now we have a new problem !!!!!!

The hot water now runs perfectly, no cutting out in shower, taps etc. BUT as soon as the cold water is turned on also, over say maybe 10% flow it cuts out the boiler !!!!!
* this happens with the shower and also any taps.

This means we can only have a red hot shower because as soon as we start to mix in the cold it cuts out before it can lower the water temp...

I have tested the switch on top of the divertor by pulling it out, this doesnt help, still cuts out.

1) replaced heat exchange
2) replaced sensors
3) checked divertor switch (by lifting it out, does this also illiminate faulty diagham?)
4) replaced faulty mixer
5) Radiator heating is perfect

We have a really good pressure of water, can anyone please explain why when the cold is also on it is cutting out?

Thanks

 

[gas4you]

What shower did you fit?

Some have to be fitted with a flow regulator in the cold side to balance the hot and cold.

Your CB24X will restrict the flow to about 9-10 l/min on the hot, so if you have very good pressure/flow, the cold could be so great it stops the hot flowing.

(If you get my drift, I know what I mean )

 

[TimB2010]

Thanks Dave,

We fitted a normal mixer, this one:
http://www.screwfix.com/prods/65957...r;jsessionid=PKOIYVKCL5RHACSTHZOSFFY?ts=82637

but it does the exact same with the taps also, even down in the kitchen near the boiler (will edit my post), so i dont think its to do with that.

can i test the pressure theory but closing the main cold water stop tap slightly?