BIASI PRISMA 28SE DHW problems

[goodwillp]

Hi, We're having a few problems with our Biasi Prisma 28SE combi boiler.

The DHW is only working when the CH on The lock out red light does not come on. It sounds like the initial start-up sequence starts but then nothing. If the CH is already on it diverts to DHW and no problem.

That said, if the CH has been on for some time and the prog room thermostat temp is reached and the CH goes off the DHW will work

If I switch off the CH by lowering the room thermostat and then try the DHW and it doesn't come and immediately try the CH it will also not come on. If I then wait for a few a minutes and re-try the CH by increasing the room thermostat.

In all cases where either the DHW or CH are not starting the red lock out light is not showing.

Due to the intermittent nature of the fault two engineer visits have failed to diagnose the problem.

Aany help much appreciated!!

thanks
Paul

 

[Agile]

Reading EXACTLY what you have said it would appear that the programmable stat has been incorrectly wired. How long ago was the stat fitted?

However, users often do not express clearly what is happening.

The first thing to check is if the system flow switch is not being operated reliably on DHW.

As there is a fault if you want it fixed then you probably need a competent engineer

 

[goodwillp]

Thanks for the response, probably badly worded so apologies for that!

The stat was wired in 2 years ago and hadn't been a problem. We've had a couple of previous problems with the boiler - blocked venturi and a torn diaphragm in both cases the red lock out light.

If I switch off the room stat and just use the timer switch on the boiler there is the same issue DHW will not light and there is no fault light. If the CH is on the DHW comes in fine.

If the CH is not on the DHW doesn't come in with no fault light.

 

[Agile]

The stat was wired in 2 years ago and hadn't been a problem. We've had a couple of previous problems with the boiler - blocked venturi and a torn diaphragm in both cases the red lock out light.

Only the venturi will cause an ignition lockout light.

Unfortunately you are confusing me by repeatedly saying the red light does NOT come on. Please only mention it if its coming on.

From what I interpret so far the first thing to check is if the system flow switch is not being operated reliably on DHW.

Tony

 

[goodwillp]

thanks Tony, Is this something I can easily test?

Paul

 

[Agile]

You need to look at the system flow switch pin at the front left and see if it promptly comes fully out when both CH or DHW is called for.

Ideally you should take the switch off and see how hard you have to push to try to get the pin to go back on CH and then DHW.

Its should be reasonably difficult to push the pin back.

Also see what themperature the gauge goes to when running hot water with the DHW temp knob at maximum.

Tony

 

[goodwillp]

Hi Tony,

I think I found the problem. I removed the flow switch and then checked the mechanics were working correctly by checking CH in the on and off position and it moved in out correctly and was firm to depress when in the out position. However, when I first checked the electronic flow switch was lying flat rather than vertical (as per the Biasi manual) and had quite a bit of play in it so I'm not sure it was making the connection correctly. I've orientated it vertically and now both DHW and CH are coming on and going off on demand

I monitor but fingers crossed

thanks for your help
Paul

 

[Agile]

The orientation of the system flow switch is totally irrelevant!

If the locating clip is not correctly fitted or is relaxed then it can cause those kind of problems.

However you have not commented on the "push" of the pin on DHW ?

Some later microswitches with the pastel blue side were a little unreliable and benefited from a very slight adjustment of the lever. The dark brown ones are fine though.

So whats the DHW push?

Tony

 

[goodwillp]

Hi Tony,

The DHW push was firm.

I think the problem was the switch as neither CH or DHW worked on Friday and just by moving the flow micro switch the both began working again fine.

I replaced the flow micro switch on Saturday and the boiler has continued to function correctly on both CH and DHW since.

thanks for your help
Paul

 

[Agile]

Well done!

A very simple solution!

Tony