Biasi 24s.... going to rip from wall !!! CH & DHW Issues

[David24S]

We are going to be moving shortly and my Biasi 24S has started playing up. We had issues a bit back and got some fantastic helpfrom here, to which I explained to the Engineer and he sorted it.
So, intermittent issue. Calls for DHW and CH, goes through all sequence but will not fire. Other times all ok, no problems and works
So it stopped working, same Engineer called round armed with 100's of schematics, boiler fired up, without him touching it.... blasted thing.
We discussed the issues and he was a bit unsure.
Now the boiler is doing this daily, I have discovered that if I move the timer switch for CH to on from off, then we get DHW, I then turn CH back to off and DHW continues.
We cannot run to the boiler and turn on/off CH every time we need DHW
I need to get the Engineer back in, but I don't need a head scratching session, and I cannot afford a new boiler before we move.
All help and advice will be much appreciated by my Engineer and myself.

Thanks in advance.

 

[Agile]

You seem to have a pretty useless engineer for doing repairs.

If you tell him to check the pump proving switch it may well be the problem.

Tony Glazier

 

[David24S]

Hi Tony,
Thanks for the reply.

Not being the boiler expert, but surely the switch for the pump operates the CH side of the system.
The DHW isn't pumped, as it's pressure is maintained by the Cold Water Mains pressure !!!!
Why would a switch on the CH pump have any bearing on the system calling but not igniting on the DHW????
Wouldn't the likely cause of the intermittent fault be the ignition board as this serves both the CH and DHW??????

Regards

 

[DP]

The DHW isn't pumped, as it's pressure is maintained by the Cold Water Mains pressure !!!!
Why would a switch on the CH pump have any bearing on the system calling but not igniting on the DHW???Regards

Boiler pump DOES run during hot water demand. How do you think the boiler heats the water that is flowing from the hot tap?

 

[David24S]

DP, Like I said in my post with exclamation marks.
Maybe it would have been better to put question marks and worded better.
I was trying to say that I thought the cold mains pressure was used on the DHW side, to push it through the boiler and then the DHW system.

The DHW isn't pumped, as it's pressure is maintained by the Cold Water Mains pressure !!!!

Thanks for that anyway, and like I said I am not a boiler expert, but ask me one on Nuclear Radiation, that's my forte !!!!

Read more: //www.diynot.com/diy/threads/b...from-wall-ch-dhw-issues.440789/#ixzz3jrCIq5Nd

 

[Agile]

I don't think that I would do that badly on nuclear radiation!

 

[DP]

When you run a hot tap, pressure drop in the secondary loop operates a switch. This switch Operates pump, pump run is checked, if ok, fan runs and ignition results. Primary water starts heating and starts flowing through secondary heat exchanger as long as hot tap is running

A heat exchanger is used to transfer heat from the primary side ( side that heats the radiators and has dirty water and is now being heated as suggested above) secondary side mean while is removing the heat from the heat exchanger resulting in hot water at the tap. Make this water flow a deluge, water only gets tepid, make it a trickle, water gets too hot and has to be temperature controlled

I trust above helps

 

[David24S]

DP, thanks for the clarification.
Glad you know what your talking about.
I thought my boiler only had one pump which was on the CH side. If you dare tell me now it has I will be totally lost !!!!

But seriously, I am a little worried that as this is an intermittent fault, it therefore could be the switch on the pump or the board supplying the switch.

Ok, so now to get my boiler geezer and his 100's of schematics back
Cannot sell the house with a dodgy combi. !!!

Many thanks

 

[DP]

Not 100% sure, but HW demand should fire boiler regardless as HW is priority over CH. If CH is off, HW demand should still fire boiler.

During HW demand, you should hear a faint hum of pump run and if sequence correct, fan run should also be heard (air emitted from the flue terminal)

Am surprised your guy is having difficulty with the boiler. If boiler does not work, finding the fault is easy peasy

Now the boiler is doing this daily, I have discovered that if I move the timer switch for CH to on from off, then we get DHW, I then turn CH back to off and DHW continues.

Page 8......Heat Request on dhw. Has noting to do with your timer. Follow the bold line.

 

[David24S]

When the boiler is playing up and no DHW, I found that if I put the timer switch to the on pos, and fired up the central heating, the hot water side then fired and stayed on after I turned the CH off. This works all the time. Every time cannot be a coincidence.

 

[DP]

This scenario would indicate where the issue lies, so your heating engineer should have no problem getting to root of the issue. The fact that the problem is there every time hot water is demanded, one does not even need a diagram to find the fault. To be familiar with sequence of operation is paramount

Easy fix

 

[Agile]

Just as I had said on Monday evening!