Biasi 24s central heating intermittent, hot water works fine

[rg55]

Hi

I've got a biasi 24s boiler which has an intermittent problem with the central heating (the hot water works fine).

So far have had the diaphragms changed, main heat exchanger de-scaled and whole system power flushed. Plumber is now not sure what the problem can be and the heating seems to work when he tests it!

When the heating works the temp goes up to about 80 degrees at which point the burner stops, it then re-ignites when the temp goes to about 50 degrees. I think this is how it's supposed to work.

When it doesn't work you just hear the pump going but the boiler doesn't click to start the burner. Turning the hot water on starts the burner and the central heating works.

Any ideas of what could be causing the problems?

Thanks

Rob

 

[Agile]

There are several possibilities all of which would need me to be at the boiler to diagnose.

I will say your plumber is very skilled at charging you for work which is not related to the problem!

Tony

 

[rg55]

thanks for the reply. Yes it would look like that(!) but to be fair on him there have been a number of issues with the boiler!

The boiler and central heating system had a load of rubbish in it, so doing the flush and de-scale were probably worthwhile and he showed me the diaphragms that he replaced and they didn't look good.

The boiler seems to be working well - it just doesn't switch on for central heating unless you switch the hot water on! I think it would have been cheaper to get a new boiler - is that worth considering? Otherwise he mentioned the "boiler stat" but said it's unlikely to be faulty. I'm wondering if it could be the PCB, which I think will be quite expensive to change.

Any help appreciated!

 

[Agile]

If you could be far more specific then I might be able to help you.

But saying 'switch on the hot water' means nothing as thats done by turning on a hot tap.

Your plumber talking about a boiler 'stat' indicates that he knows nothing about boilers as later boilers dont have 'stats'!

Tony

 

[rg55]

Hi Tony

sorry for not being clear enough but I did mean just that as turning on the hot tap seems to kick the boiler into action. The central heating then seems to work - all the radiators come on and the temperature gauge keeps cycling - starting at about 50 degrees (when you hear a click that seems to start the burner) to about 80 (when the burner cuts out). What further details would you need?

Yes the plumber is an old guy(!) but I do trust him even if his terminology isn't always current. I thought he meant the temperature sensor when he said "stat" - could that be the problem?

Thanks

Rob

 

[Agile]

I still dont know what you are doing!

You turn on hot tap and get hot water!

What do you turn on to get heating?

The temp sensors will not stop your boiler working unless they were low resistance which is not a normal sensor fault condition.

Tony

 

[rg55]

sorry - here's what I'm doing:

1) Boiler set to provide heating and hot water (think it's winter mode)
2) Heating doesn't come on (even if radiators are cold)
3) Open tap and get hot water from it but this also gets the central heating working!
4) Heating seems to work fine for some time but then after a while goes back to step 2) of not coming on

This just doesn't make sense - it's almost as if the boiler doesn't know it has to provide heating until a hot water tap is turned on!

The hot water works perfectly - the boiler turns on every time a tap is opened. It's just the heating that is behaving strangely. You don't need to leave the tap open for the central heating to work - just opening it and closing it seems to get the heating working for a while.

Thanks

Robin

 

[Agile]

The pin on the pump proving pressure unit is not coming out far enough to reliably operate the microswitch!

Why can your nupty plumber not see that?

Has he ever checked that the eye of the pump is clear?

Tony

 

[rg55]

Hi

thanks for the reply tony. Plumber came today but couldn't fix the issue.

He confirmed that the main flow switch was working (think that's the same as the pump proving pressure unit you mentioned). He said that the hot water wouldn't have worked if the switch wasn't working.

He also checked the pump, which seemed to be working.

Noticed that the burner doesn't fire unless a hot water tap is opened or the pressure release valve opened. The bypass valve also seems to be hot all the time - is this correct? (all radiators valves are open). Pressure is set to 1.5bar.

Plumber is planning on trying to flush the boiler (to clean any more rubbish from it) and possible try a new pump. Is this a good plan or should we try something else?

Thanks

Rob

 

[Agile]

Oh dear!

He seems to have little ( no ) understanding of boilers!

If there was any problem with the pump then there would be no hot water!

Could YOU do a little test before you let him in again?

Set to CH and then remove the plastic flow switch housing and use a cocktail stick or similar to push through the hole to activate the lever on the switch.

If that does not get the CH going then telephone me! But there is an anticycle delay of up to three minutes so you may have to wait a little.

Tony

 

[rg55]

Hi Tony

thanks for the reply. I've downloaded the manual and have been ploughing through it to try to work out what's going on!

Is it the main circuit flow switch that you told me to check? If so then I saw the plumber test it already and nothing happened when he pressed the switch - the boiler just sat there with the pump going but the burner didn't light. He even showed me the switch working when it was attached - a pin pressed out to make the contact. The only thing that got the burner to then light was opening a hot water tap or as we found out yesterday the pressure release valve!

I'm no expert but I don't think it's the pump either(!) as once the boiler fires up the first time the central heating keeps working with the burners firing without you doing anything else.

Could it be dirt in the boiler? - it's just that after he flushed the system bits of dirt keep coming out of parts of the boiler when he drains them.

Thanks

Rob

 

[john gill]

Exact same problem, what was the outcome.

 

[terryplumb]

John gill ,you will be better off starting a new thread mate , as this one had no conclusion 5 years ago.regards terry.