Alpha 240E intermittent HW / Anyone have a manual?

JohnPaulCain · 27 Sep 2006

Hi all

I would be grateful for some advice. I have recently moved into a new house with a 7 year old Alpha 240E combi. The HW works intermittently, it stays on for 10 or so seconds then goes off for a minute then comes on, Very annoying! I have tested the flow rate and I have about 12.5 l/min, it seems to stay on longer at lower flows?

Anyone know what it could be? I was thinking faulty flow switch but haven't looked yet.

Also does anyone have a manual they can email me?

Any help would be gratefully received!

Rob · 27 Sep 2006

sludge in dhw HE?

Gasguru · 27 Sep 2006

Does the hot water demand light stay lit whilst the hot tap is open?

If it does the problem is often caused by a faulty flow thermister or a blocked secondary heat exchanger.

Does the boiler work OK in heating mode, with the heating temperature turned up to max?

Agile · 27 Sep 2006

Your boiler can only heat about 9 litres per minute by 35 C so at your flow rate the hot water would only be warm even if it was working properly.

I agree that it may be the secondary HE is blocked but a competent boiler engineer would have several things to check before coming to any conclusion!

Tony Glazier

avidfan · 28 Sep 2006

Common problem with the 240 and 280 Alphas. It's usually the hot water sensor but sometimes the primary one.

JohnPaulCain · 28 Sep 2006

Thanks for the response all.

I am not sure which light is the demand light as I don't have a manual?

The boiler seems to work fine in htg mode.

As regard flow rate and temperature it's a bit strange, I understand 9 l/min is the design flow rate and at 12.5 l/min we should have a temperature rise of only 26.25 Deg but I am sure the water is warmer than 35 degs, maybe my boiler is exceeding design! (Or I measured the flow rate wrong!)

Agile · 28 Sep 2006

The boiler can be set to any power output!

However, the manufacturers lay down the operating parameters and running it at a greater power input is liable to damage it and is classed as At Risk in gas safety terms.

Tony

ChrisR · 28 Sep 2006

You can check the gas rate at the meter. Time 1 cu ft or 1 minute and do the sums. Tricky if it's only on 10 seconds, though! If it IS burning too much gas on HW it wouldn't be surprising if it's overheating.

They say 2.74 m³/h (96.76 ft³/h). Bit precise!, say +5 to -10%.
A phone call to alpha and you'll have the manual next day.

JohnPaulCain · 28 Sep 2006

Surely the gas valve would only let a certain volume of gas through though right (assuming standard operation)? Wouldn't this be limited?

I am not sure if my boiler has been modified at all. it was supposed to have been serviced by a CORGI guy before I bought the house, would there be anything on the documentation?

JohnPaulCain · 28 Sep 2006

ChrisR said:
If it IS burning too much gas on HW it wouldn't be surprising if it's overheating.

This was my concern initially, I thought there might not be sufficient flow. This doesn't seem to be the case though.

If it was overheating would the boiler cycle or trip out on overheat?

Sorry for guessing things but I haven't got the manual, will ring alpha today though, thanks.

JohnPaulCain · 29 Sep 2006

This morning I had a long hot shower! 2 minutes after the wife had a hot/cold/hot/cold shower.

I looked at the demand light and it is on constantly when a hot water outlet is opened. However the boiler fires and goes out intermittently.

Does this eliminate the possibility of the flow switch being faulty? I assume the flow switch is linked to the demand light?

ChrisR · 29 Sep 2006

Yes. 90+% of the time it's a combination of sludge in the secondary heat exchanger or on a sensor, the sensor(s) themselves or in your case maybe gas rate too. £100 fix.

Agile · 29 Sep 2006

If its a sludged plate heat exchanger then its 136 pounds at our London prices, eighty four if gas rate setting and ninty seven if a sensor.

I had an interesting repair yesterday! So typical of a blocked HE and it was fitted by an unreg Polish fellow. Due to parking difficulties I was in a hurry and removed the plate but it was shining clean just like a new one!

I tested the DHW sensor cold and it was the correct at 12 k.

What should I have done next? I will add that I was strapped for time because the boiler could not be isolated from the supply and I had to disconnect the choc block live.

Tony

doitall · 29 Sep 2006

I have a manual if the OP emails me.

ChrisR · 29 Sep 2006

I'd be measuring temperatures - is it actually getting hot? Checking CH, modulation, water flow rate, aps etc couple of suchlike normal things which aren't "interesting".
Does a crack in the track on the HW setting potentiometer count as interesting?
What was the boiler?

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Alpha 240E intermittent HW / Anyone have a manual?

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