Combi boiler - fluctuating water temp

[Edinburgh1]

Hello all. Novice here, so go easy

Combi boiler approx 8 years old. Central heating perfect, touch wood. Plenty of hot water in downstairs taps (kitchen, WC) and upstairs bathroom basin. However, water runs tepid in bath after approx 5 seconds of hot. System keeps dropping pressure and the 'outflow'? pipe dripping outside.

Suggestions so far have been either or both of the following.......

Replace heat exchanger as it's clogged up and can't service the greater flow of water needed for bath...

Replace diverter value.......but not sure why?

I can survive the way it is until after Xmas, but would appreciate some guidence before I call out a plumber.

Cheers guys & gals,
Alan

 

[picasso]

what boiler do you have ?

 

[Edinburgh1]

Hi. Should have included that! Its a Valliant. Don't have manual but guessing at turbomax. Also this has been going on before the cold snap, so don't think the extreme temps here in Scotland have anything to with it. Cheers.

 

[picasso]

depends on the size of your combi, if you have a 24kw it will struggle to fill a bath at any time of the year, to check the divertor valve you need to let the central heating cool down, the when you run a tap feel the flow pipe under the boiler, if it starts to get hot then the divertor valve is passing, it also might be a good idea to have the boiler serviced as the expansion vessel may need attention.

 

[spraggo]

If you reduce the water flowing from the bath tap until it comes out about the same flow as the basin tap the water should get hotter, you will have to bear with this until the incoming mains cold water rises in temp, but get that leak fixed by fitting a new pressure relieve valve.

 

[ronp849]

Hi -I had a similar problem with a RavenHeat Combi. (Mind you, It had been running for about 15years).

The Central heating/Hot water was working fine but it would not hold pressure. Kept on discharging through the boiler pressure release valve.

It turned out to be the Expansion chamber - This needed to be pressurised, (air), to about 7psi. I checked and it was zero. I removed the whole expansion chamber and the schraeder valve from the air filler stem and cycled the pressure a few times to remove any water condensate. Refitted the valve and repressurised to specified level. (This was left alone for a couple of hours and the pressure rechecked to make sure the air had not leaked away).
Once checked ok, the expansion chamber was refitted and the boiler was fine for another 5 years.

Ron

 

[nick000]

Hi Ron,

I have exactly the same problem with a Ravenheat boiler which is also about 15 years old. Keeps discharging through the overflow pipe to outside, have to manually release the pressure, and the water temperature in the shower fluctuates.

I don't have the skills to do what you describe though to fix - not without a step by step! Any idea if there are any good guides to doing what you describe or otherwise any idea how much it might cost to get an engineer to fix it? Been searching everywhere online for what might be causing it and yours is the only post which seems to describe my problem exactly.

thanks a lot
Nick

 

[Kingsway]

Hi Ron,

I have exactly the same problem with a Ravenheat boiler which is also about 15 years old. Keeps discharging through the overflow pipe to outside, have to manually release the pressure, and the water temperature in the shower fluctuates.

I don't have the skills to do what you describe though to fix - not without a step by step! Any idea if there are any good guides to doing what you describe or otherwise any idea how much it might cost to get an engineer to fix it? Been searching everywhere online for what might be causing it and yours is the only post which seems to describe my problem exactly.

thanks a lot
Nick

Expansion vessel has lost its air. It would need draining of water and re pressurised to 0.75 bar. Also sounds like the plate heat exchanger is scaled up causing temp in shower to fluctuate.