Intermittent Hot Water Alpha Boiler

[Lancashire Lass]

This past week we've started getting problems with intermitten hot water supply from our boiler. It's an Alpa C23 combi boiler. Sometimes we open the hot water tap and the water heats up nicely within a matter of seconds and then all of a sudden, mid-flow, the hot water will run ice cold and remains that way. We've checked the indicator neons on the boiler when this happens to see if there's any fault being reported but the indicator neons are all lit the way you'd expect them to be and showing nothing untoward.

If we turn off the hot water tap when it happens, leave it for a minute or two, then turn it on again the water will run hot again within several seconds.

Any ideas what could be causing this to happen?

 

[Billy Bob Bob]

could be many things causing this fault,without the opportunity to test the boiler start with getting it serviced if its needed ,see what that throws up

 

[tackleburger]

Flow switches are common fails on these boilers. It may be worth checking you gas supply is full on. I had one that was doing this and a box in the cupboard had fallen and knocked the control lever to nearly off.

 

[Paulplumb]

Did you get the leak fixed on this boiler?

 

[ferret]

does it get hot again if you reduce the flow from the tap if so it could be gas valve adjustmant as it should modulate with the fow , if it does it could be a faulty flow switch but this should show on the neons with A on and B flashing

 

[Lancashire Lass]

Did you get the leak fixed on this boiler?

We've had the company back and (fingers crossed!) it looks like the leak has been fixed. Looks like it might have been a faulty automatic air vent valve.

 

[Lancashire Lass]

The boiler was serviced mid-July 2010 and the DHW flow switch, pump and automatic air vent were replaced at the time of the service as they were faulty (fault shown on neons with A on and B flashing). And, no, it doesn't get hot again if we reduce the flow from the tap. It's a bit of a strange one this, really, as there's nothing untoward showing on the indicator neons but we're still having intermitten problems with the hot water supply.

 

[aggis]

Hi, 1st thing to check is the dhw ntc [sensor], should give 12-14 k ohms cold, replace if necessary.
Then the modulation of the gas valve should be checked [ does the flame go up & down, when running hot water ]. 11mb high & 2.5 mb low
This would be best checked by a G S engineer [pressure & voltage readings at modulator coil on gas valve,approx 9v dc high & 2v dc low]
If the voltage is going up & down but the burner stays stable, [at max pressure], check resistance reading on the modualing coil 45 ohms, if out, the gas valve requires changing.
Reason.... if the boiler calls for hot water & does not modulate, stays on high the overheat cuts the burner off & there's a delay till it resets.