Ariston combi A , hot and cold water

[Adrian80]

hi,

I have an ariston combi a boiler, it's probably 10 to 12 years old, and when we run the hot tap in the bath it goes hot and cold, and you can hear the boiler firing up and down when it does this.

Last winter we had the domestic hot water heat exchange replaced and that seemed to cure the problems. However it seems to have come back, which is disappointing.

We live in a hard water area, and the heat exchanger seemed pretty blocked when it was removed last time. However I can believe it's become blocked in such a short space of time.

The ch is effectively new installed 8 years ago and then extended 2 years later. So I can't imagine there is to much crud floating around the system. We also have a fernox tf1 installed, which is always very clean.

Is there anything else likely to cause this behaviour.? Or do I suck up for another heat exchanger, or try and clean the existing one, with after fernox descaler? Or God forbid, new boiler as 10-12 years is the life of a combi?

Thanks for any advice.

Adrian

 

[mcmoby69]

If I was changing a crudded up plate heat exchanger I would advise a full drain and system flush plus a filter on the return.
Were these suggested?

 

[Adrian80]

Thanks mcmoby.
The system was fully drained, and we have a tf1 fernox filter on the return, which does magnetic and non ,magnetic debris.

Draining the system is always a pest, as the boiler is upstairs and all the pipe work drops to each radiator down stairs, but I think these act as gravity traps for any crud in the ch side of things, in addition to the filter.

 

[mcmoby69]

could be the pump losing its oomph!(tech jargon )

does the diverter move properly?
to test this system needs to be cold.
turn hot tap on, does flow pipe to rads warm up?

might be time to get yet man back in

do the rads heat up quickly or slowly, does the boiler cut off before rads are hot enough?

 

[Adrian80]

Hi mcmoby,

I will test the diverter valve this evening before the heating swtiches on. I assume if the flow or return gets warm, its a sign the diverter valve might be malfunctioning or the diagphragm has a hole in it.

Rads all fine, get very hot very quickly.

I think the pump is electronically controlled and i did see in the manual that you can turn the speed up, which might give it a bit more oomph! i assume i have correctly understood the technical nature of oomph!

I had a look at the TF1 filter this morning to see if the system was really sludged, but despite the water being a bit black in colour, it was nothing like the thick soup you can get out the bottom of a radiator.

After flushing the filter i topped up the pressure, and tested the hot water and it seems to have cured the problem. Therefore i wonder if the pressure release valve might be failing a little. I assume if i put a balloon on the exit pipe and i get some discharge this would be a strong indication of my problem, or there any other obvious ways systems can loose pressure? There are no leaks in the pipework as far as i know.

Many thanks for the suggestions.

cheers
Adrian

 

[Adrian80]

So after running the kids bath, the flow and return are stone cold. However, the fault appears to have disappeared, which makes me think re-pressurising the system might have solved the problem.

Is it normal for ch systems to loose a bit of pressure over a year? Where does the water go if there are no leaks, or I guess no visible leaks. Or very small leaks which just evaporate rather than making anything wet.

Until we get some freezing weather I suspect the fault won't reappear.

 

[mcmoby69]

If your boiler is the highest point of the system and you have lost water, air will collect in the boiler.
This usually causes excessive noise, overheating and cutting out.
If you have topped it up and the air has moved into the system it is possibless you have sorted it.
Rads might need bleeding and topping up.

Slight leaks will evaporate and a once a year top up is not excessive.
Is it due a service? Get the expansion vessel checked!

 

[Adrian80]

The boiler is joint highest point with some towel radiators and column radiators,'which always seem to collect a bit of air.

Service is imminent, so will ask him to take a look at it all

Cheers for the advice.

Adrian