Alpha CB50 runs cool - please help.

[stevefromnewcastle]

If anyone can help with our problem I will be eternally grateful. Here we go....

Approx a year ago we extended our house and had a new Alpha CB50 boiler fitted to cope with the new rads etc. The hot and cold water piping was extended to serve the new rooms. The boiler is fairly high capacity. The brochure quotes a “never ending supply of hot water” and a flow rate of up to 18 litres a minute.

The main problem is when running a bath, the water runs very hot for approx 5 mins (we think until the reservoir is empty) then it cools down to luke warm and the flow rate reduces. The boiler should start up and keep the water hot. After a few minutes it goes hot again but the flow is still low.

We have had Alpha engineers in who say there is nothing wrong with the boiler (3 times). They say that there is a shower or mixer tap on the system where cold water is leaking back into the hot water. Our plumbers are sceptical but as the recommendation of Alpha have fitted a non return valve on the hot water output from the boiler – it hasn’t solved the problem.

The confusing thing is that the hot tap in the kitchen and the bathroom work fine. They will supply hot water constantly. I have tried excluding any mixer taps etc from the system by turning off the isolation valves. The only device I can’t do this with is the shower as the pipework is behind the tiles.

As the Alpha engineer insists it is the shower at fault, I sourced a new cartridge for it but the problem persists.

Another possible clues:
The boiler overflow (I think it’s the pressure relief valve) drips constantly (24/7)
When running the bath the radiators cool down

Hope I have included all relevant info. This has been driving us mad for months so any help greatly appreciated.

 

[GforceJames]

If I remember rightly these boilers have two prv's one for the system and one for the unvented store.

Can you identify which one is letting by, could be a faulty thermistor or dirty plate HE, at a guess.

James

 

[Agile]

I suspect you are confusing a storage combi output with the actual underlying boiler output. Very few people seem to be able to understand the limitations of these systems.

Without visiting your installation, which you are not going to pay me to do, then all I can say is to measure the flow rate and temperature of the hot water.

Many of the boiler manufacturers are very naughty as they quote the initial flow rate as if they are maintained continuously.

Tony

 

[stevefromnewcastle]

Thanks for the reply James. Not sure what you mean or how I can tell which one it is. The Alpha engineer has checked the boiler 3 times and it isn't old. He reckons the boiler is working fine.

To quote the brochure:
Unique automatic flow regulator means hot water never runs out.
After filling a bath – if there is still a demand for hot water, the CB50’s automatic flow regulator controls the flow to keep the water hot. The Alpha CB50 will therefore always provide hot water no matter how long the hot tap is left open, unlike some other storage combis – so you can run a shower immediately after filling a bath with no problem!

Are they telling porkies or is there really something wrong? I don't understand why the hot water is constant from the sink taps but not the bath. They are both fed from 15mm pipes.

 

[lawrenso]

Hi Steve,

did you have any joy with this, we are having the same issue, with our shower actually going stone cold tonight. My wife stopped the water and got out, I reset the boiler and then there was hot water...

Cheers

Steve

 

[stevefromnewcastle]

Hi. Sorry for the delay, been working away from home.
No real solution to this yet. Our shower is fine now, it's the bath we have a problem with. Maybe it is the high flow rate of hot water that is the problem.
I suspect your problem is different as your hot water stopped completely. If you find the answer I would be interested to hear it. It may shed some light on ours.

Cheers

Steve