Biasi M90e.24S Hot water problem

[rayfacc]

Hello,
can anybody help.
I have a three year old combi as above.
A gradually worsening fault over the past few months has been sporadic non availability of DHW.
Last week it got much worse so I got a CH engineer in. He found that the diaphragm was apparently operating, pushing the pin out when the hot tap was opened and operating the micro switch, which in turn started up the heating sequence, all hunky dory. EXCEPT, sometimes even while the hot tap is still open and water sounds as if it flowing thro the valve, the pin goes back in and of course the micro switch does as it is told and aborts the heating sequence. The engineer thought that possibly the diaphragm although not showing any visible damage, may have been dicky, so he fitted a new one just to be sure and took three tenners off me because when he left the system seemed to be working properly.
Of course before he reached the end of the road it had reverted to its previous form and now hardly works at all when the DHW is demanded.
Any advice would be appreciated because the dreaded call out charge makes speculative diagnosis rather unattractive especially in these credit crunched times.
cheers and regards to all the DIYnot community.

 

[Agile]

It sounds as if there may be dirt in the eye of the pump! Check this first!

If not then the plate HE may be blocked, this can be evidenced by the temperature scale going above 70° on DHW.

Lastly, just possibly the injector screw is loose.

Tony

 

[ChrisR]

This can also be an air problem.
Try
Make sure the cap on tha Auto Air Vent , 21, is loose a couple of turns:

That could be all it is. Otherwise, open a a drain cock on the pipework, to let out some water until you can hear air being drawn in to the AAV. This may be a bucketful or so. Close the drain cock but leave te AAV open.

Open the filling loop slightly, so water enters the system really really really slowly. If it takes a couple of minutes, fine. Stop at say 1.2 bar, and try again. If the AAV weeps water out, it'll have to be changed.

 

[rayfacc]

Thanks Tony & ChrisR, for your suggestions.
I had a CH engineer in this morning and he spent a lot of time checking it all out. His conclusion is that the Heat exchanger may be blocked by some debris from the radiator circuit, reducing the water pressure through the valve and causing the op. pin to retract. The rads. are the original ones about 35 years old, and we live in one of the country's softest water regions. I don't know how debris in the CH circuit might block the DHW circuit, do you?
Funnily enough when he removed the microswitch from its mount on the water valve pin and operated the switch manually,while a tap is opened, it all works OK as long as the microswitch is held closed. DHW heats up, flow rate perfect etc.
Perversely, the CH appears to be working fine, which might seem to contradict his conclusion about the heat exchanger.
We still are not much further forward.
cheers [/i]

 

[Agile]

Didn't he or you inspect the eye of the pump?

You are misinterpreting what he said.

Sounds a useless sort of person to me if he comes and leaves without fixing it!

Tony

 

[rayfacc]

Thanks Tony for your continued advice,
No WE didn't check the "eye of the pump" because HE dismissed this as not being a likely source of the fault.
To do it myself do I just remove the central screw and check inside or what? Does the water supply have to be turned off first?

BTW.
The CH is now behaving erratically, not coming on as promptly as it had previously, green lamp flashing about 2X per sec. while off, then normally when burner does decide to fire up.
over to you, and I do value your expert advice.
regards
Ray

 

[ChrisR]

green lamp flashing about 2X per sec. while off

Doesn't it just do that while lighting - I can't remember.

In what way is it erratic - how long does it flash twice a second?

There are lots of reasons why the primary flow switch might not operate fully and quickly. Lack of flow IS one of them, so if the boiler side of the tap water heat exchanger is blocking, it's very possible for it to cause a problem.

The "eye" of the pump is inside, and wet. The centre of the impeller.

Apparent lack of circulation means one of
lack of pumping effort
blockages, or bypass open
fault in detection mechanism
trapped air.

Each one would take a lot of words to explain fully! This particular boiler IS pretty fussy in this department. You need someone who has seen a lot of them.

 

[rayfacc]

Thank you ChrisR,
Noted.
Ray

 

[Agile]

The eye of the pump is the easy thing to check and therefore the first to do.

Tony

 

[rayfacc]

Hi Agile & ChrisR,
Decided to have a go myself, so removed the pump. captured the water that escaped and found a small amount of debris at bottom of pail.
Cleaned & refitted pump, bled at front screw, and eureka the DHW started up, several times. CH OK also. At time of writing have operated DHW about 10-15 times, works perfectly.
Muchas gracias for the help, wonder how much the Biasi agent might have charged me?
best wishes
Ray

 

[Agile]

Did you look at the eye of the pump for dirt trapped inside it?

Tony

 

[rayfacc]

Eye Tony, eye did that as you suggested already, gave it a good old fashioned seeing to with a brush & running(cold) water.
yours eye
Ray