Alpha 280e Boiler Short Cycling

[londonboards]

Yes, another boiler short cycling thread!
I have an Alpha 280e boiler.
It gets the radiators up to temperature quickly. The radiator return pipe is hot, not as hot as the outflow but hot. After it's up to temperature, the boiler will fire for 30 seconds then cut off and go through its 3 minute wait cycle and fire again for 30 seconds or less. Water and radiator thermostats on about half way. Turning the radiator water temp down decreases the radiator temps but increases the number of times it cycles on and off.

New parts fitted to date:
Main heat exchanger
Plate Exchanger (water heater exchanger - no crud in old one)
2 x thermistors
1 x flame height probe
Over heat thermistor
Air bleed valve
New PCB

I'm thinking the burner is kicking out too much heat. Although the modulation works well I don't know if gas pressure is still too high. Do I need a gas pressure test?

Or is this type of cycling OK?

Radiators get up to heat (hot to touch) in all rads and hot water works well. So I'm thinking water flow through the radiators and the pump is good.

Fan seems to work OK but maybe its not getting the burner heat out quickly enough.

Any suggestions.

I'm a mechanic/engineer and I can use a voltmeter.

 

[ianmcd]

have you set the CH output to what your home needs ? it is done on the pcb and you say you have changed the PCB did you set the new one up, factory default is maximum which unless you have a very large house you would never need.

 

[londonboards]

That’s a good point. There are 2 small potentiometers on the PCB. One of them modulates the burner and the other one doesn’t seem to alter anything.

I adjusted the burner one so that it modulates the boiler down to quite a small flame. With that and the control panel thermo to low (about 33% on) the flame is very low. But it still cycles every 30 Seconds of burning or less.

Flow temp is 32 deg C out of boiler and 26 deg C on the return.

If flue or fan overheating, would that turn off boiler and make it cycle?

Greetings. Richard.

 

[londonboards]

And if I turn up the boiler termo to full
blast, I get a water temp of up to 70 deg C but after 10 mins I get overheat cutout.

Overheat temperature is about 80 deg C. Which I’m guessing is about right.

 

[ianmcd]

I have seen this happening on these models and an easy enough fix but as it involves opening the Combustion Chamber, we are not allowed to give that advice on the open forum

 

[londonboards]

This problem has been with this boiler for a while. The combustion chamber linings have all been replaced. Looks nice in there.

 

[gas112]

Not being funny but why would anyone spend that sort of money on a 20 year old boiler parts are a fortune for these old alphas and yep one of first things a gas guy would have checked is hi and low settings ,takes 5 mins

 

[londonboards]

Yes it's an old boiler. I've spent about £250 so far and the rest of it is in tip top condition. Why spend £3,500 (which is what I was quoted) for a replacement? I reckon to get another 5 to 10 years out of this boiler. I have all the parts to do any repairs and I'm now completely proficient at replacing any of them if something else goes wrong.

I recondition 40 year old motorbikes in the main and I apply the same criteria; why chuck something away when it can be fixed and made to last.

And I get a tremendous sense of achievement by doing so.

 

[gas112]

250 quid on bits could you give me name of supplier i would love to get all those alpha bits for that price trade price would be triple that at least, if available as some are now getting obsolete
The rest of it is in tip top condition there isnt much more to it
Proficient at replacing them ! but its still not working so pretty pointless changing parts .
They were a good boiler and are about the most simplest to repair baxi 105e was a clone of it.

 

[londonboards]

Yeah they were recon bits. £60 for the plate exchange, £45 for the PCB and thermistors and so on are cheap. Just look on eBay. Right now someone is selling all three PCBs for £25. That's worth a punt.

Ebay Alpha Boiler Parts Search

Working perfectly now. PCB not doing the modulating. Replaced and now it is.

Just need the gas engineer to check the burner pressures and the job's a good'un.

The problem with these old boilers is that you can't find an engineer who wants to deal with them anymore. And it's understandable. It takes a lot of time researching the parts, getting them and fitting them and customers don't want to pay that kind of money or put that kind of money into an old boiler.