Alpha CB24 Hot water-not hot enough even on highest temp stg

eccoboy · 15 Feb 2007

Hi folks, I was wondering if anyone could help me on this one. The hot water basically doesn't get hot enough (i.e. when I run a bath the water is just luke warm) even if I adjust the HW temp setting to the highest setting (point 9) Just for info, the water does increase in temperature if I reduce the flow of hot water on the tap to less than half.

Is there something I can check. I've previously had to replace the thermistors, both primary temp sensor and DHW sensor and a new DHW switch so I'm reasonably happy undertaking the work. (p.s. don't worry, I used the white thermistors rather than the old blue ones which apparently are of poor quality)

Any help really appreciated, many thanks Ben

Agile · 16 Feb 2007

You are probably expecting too much when the incoming water is only about 6°C !

A 24 kW boiler can only heat about 8 litres per minute to be just too hot to keep your hand in for more than five seconds.

Have you measured your flow rate?

Tony

Slugbabydotcom · 16 Feb 2007

Bear in mind that there's a few possibilities here but just wanted to share the experience of a job a few weeks back with the same boiler and the same symptoms.
I checked the burner pressure which was just 2 mb.
When I checked the working inlet pressure I found that again the pressure was at 2mb!
The gas pipe was undersized. 15mm for the whole of a 12m+ run but even that wouldn't allow for such a great pressure drop.
I disconnected the meter outlet thinking that it may have been blanked and that the blank may have buckled when it was fitted thus allowing a small amount of gas through.
Turned out to be sulphidisation in the pipework which fell out in a heap when I took the pipe off.

I had no choice but to disconnect the supply

eccoboy · 16 Feb 2007

Hi chaps, thanks for coming back to me on this one. What is strange is that the boiler used to produce buckets of hot water (really hot water that is ) even when the HW setting was set to only about 6-7 on the user dial. I must be able to get the boiler to reproduce this level of performance somehow.......

Any help greatly appreciated indeed......cheers BB

scatmanjohn · 16 Feb 2007

What is strange is that the boiler used to produce buckets of hot water

Was it in the summer time per chance?

eccoboy · 16 Feb 2007

No Scatman, the boiler has always been spot on, not just in the summer months........

scatmanjohn · 16 Feb 2007

eccoboy said:
No Scatman, the boiler has always been spot on, not just in the summer months........

If you can measure the flow rate at the tap (litres/min) and measure the water temp coming out of the hot tap and also the temp of the cold water we will have a starting point.

Paul Barker · 17 Feb 2007

Yes, you have done all the right things, the old flow switch was upgraded and the thermisters are upgraded. No other common problems on that model which could cause your worstening performance, so you are looking now at checking max dhw operating pressure, working pressure as mensioned, actual performance not "it isn't like it used to be".

IF after setting up correctly the actual measured performance is not as Tony idicated for this time of year. then we have to consider cleansing the system and especially the plate heat exchanger or renewing it.

eccoboy · 17 Feb 2007

Thanks for helping me out on this one fellas. I know that this might sound like a really dumb question but what's the best way to measure the flow rate? Do i just run the tap into a bucket for a minute and measure it that way? If so I'll measure it tomorrow and post the result on here along with the temperature readings.

Cheers Ben

ChrisR · 17 Feb 2007

eccoboy · 19 Feb 2007

Righto chaps, sorry for the delay, thought I had a thermometer at home but ended up borrowing one from work today.

Flow rate is 9 litres per min
Cold water temperature is 10c
Hottest water running at 9 litres per min is just 39c

Does this help identify the possible cause?

Cheers Ben

scatmanjohn · 19 Feb 2007

When you run the taps does the central heating flow pipe get hot?

HarrogateGas · 19 Feb 2007

yes the divertor valve is passing or the plate heat ex is scaled.........not drastically though. your not far off your 35degree rise

eccoboy · 19 Feb 2007

Actually, yes, the heating pipe out does get hot, does that help?

HarrogateGas · 19 Feb 2007

definatly sounds like the divertor valve is slightly passing, not by much though as the DHW temperature rise is not too far off the mark.

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Alpha CB24 Hot water-not hot enough even on highest temp stg

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