biaisi combi cycling when timer off?

[jime17]

Hi all.
Firstly some info. 3 bed terraced house. Hard water area.
Biasi m90f 32s gas combi boiler (i know they arent the best) installed oct 2004. 7 rads. honeywell main thermostat (just a turney one with bi-metallic strip) optima trv's on all but hallway (where termostat is) and bathroom. Only alterations to system have been moving bathroom rad about a year ago to new position on adjacent wall approx 3ft away and seemed to have no adverse affect.

Have had most rads off for decorating and to cure leak from where collars screw into rad body. last was about 6weeks ago, but doesnt seem to coincide with my problem which is as follows.

The timer is set to come on for 1.5 hrs at 5am and then from 6pm to 11pm.

When It switches off at 11 and I am in bed, every so often for a couple of hours the pump seems to start itself for a few seconds and then switch off. usually a couple of times in sucession, then a lull of 10 or so minutes and then again. Sometimes the actual burner seems to fire up as well, but not every time. Then after a couple of hours it seems to stop.

Any ideas would be appreciated.

Jim.

 

[fitz1]

has ur boiler got a small hot water storage.

 

[jime17]

if you mean, does it keep a small amount of water hot to prime the hot taps, then no.

(thanks for a quick response)

 

[Agile]

It seems that there is an actual or assumed demand for hot water or heating.

Take the front cover off and try to locate the Hall effect sensor on the right side of the gas valve. If you turn on a hot water tap you will see the red LED illuminate.

Check that this does not come on while there is no hot water demand.

When you go to bed turn the blue tap underneath clockwise 90° and see if the boiler fires up over night.

If it DOES NOT then you have an unexpected but actual demand for hot water during the night.

If it still does then let me know and I will devise another test for you to identify the fault.

Whats the serial number?

Tony Glazier

 

[jime17]

Hi Tony (and everyone else)

I will try that tonight. I think the blue tap shuts off the dhw doesnt it? So I assume by isolating the dhw, you can discount anything asking for flow of hot water? (sorry if thats rubbish. I'm just trying to get straight on my head what I'm doing)

the serial No is N106621003 GB

it also has a GC No 47-970-22

just as an aside I have a water meter which when no taps etc are turned on , the needle is absolutely stationary, so I'm assuming there is no leaks in the system.

Jim.

 

[Agile]

You dont say if you have done my first check on the red LED. Thats quite important!



Let me know the outcomes!

Do you have a very modern washing machine with digital display? Or a water softener?

Tony

 

[jime17]

Right. sorry for the delay. been away at the weekend.

I just fired up the boiler for 30 mins and took the front cover off. I then waited for another half an hour and the bloody thing hasnt done it once! I turned on the hot tap and the led came on immediately, but the problem hasnt arisn as yet.

the only things i've done are clear a little bit of walpaper out that must have fallen down the back when decorating and bled the bathroom towel rad which had a bit of air in. not a great deal just a few secs. I also let a bit more water out as the pressure har risen to 2 bar which I thought was a bit high?

 

[jime17]

right.

took cover off. when boiler pump fires for a few sec with timer off. the red light does not come on. whne I turn the blue tap. it seems to do it slightly more often I think. i can hear a relay click every time it turns on.

by the way, washing mechine is not on same water supply. and itts not a new one anyway.

 

[Agile]

If you dont use the boiler the PCB will run the pump for a few seconds every 24 hours the keep the pump from seising up.

Tony

 

[Gasguru]

I wonder if you have a dead leg on your pipework and you are on a shared main.

I repaired a Puma years ago and the boiler would fire up on its own briefly, the owners said it had been doing this for years. It was due to a dead leg on the pipework.

Every time the neighbours used a tap the water inertia after they closed a tap would compress the air in the dead leg and fire up the boiler.

 

[Agile]

He appears to be saying that he has seen it fire up but when it did this the red LED on the Hall effect flow sensor did not operate. If he is correctly reporting the situation then its not the dead leg problem.

A long shot but if the timeclock cable connection is disconnected then the boiler will by default fire up on CH. A simple check on the connections at each end would eliminate this remote possibility.

Delving inside the boilers electronic controls box should only be done by a competent person.

Tony

 

[jime17]

Tony, what you are saying is right. When it fires up sporadically, the led does not glow.

It does not appear to be firing/pumping at regular intervals such as the pump working every 24h to stop it seizing. I've just got out of the shower (the timer is off so no ch) and its doing it now. It seems that when it cools down that this problem stops. When this problem occurs sometimes the pump will start whirring for half a sec, sometimes its a few sec and the gas will ignite.

When you mean competant do you mean gas wise or electrically? I have an onc in electrical engineering, but i dont know a great deal about gas see.

 

[Agile]

No, I meant competent to open the electronic control housing. Its more like computer insides.

Electrical Engineering is not quite the same skills as historically thats biased towards heavy engineering and not electronics.

So if you would change a graphics card on a PC then I would expect you would have the necessary skills.

When you have exposed the PCBs then watch the three diagnostic LEDs when it fires up in error and you can by reference to the book see if it thinks theres a demand for CH or DHW. Its better to learn the sequence by test firing so you can immediately see which of the two it is.

Note that the plug on the back of the clock is not coded and can be fitted backwards or displaced. Before removing it note very carefully which way round it goes.

That is a long shot but apart from a faulty Hall effect sensor or main PCB I cannot suggest much more until you have determined if its a CH or DHW demand.

Tony

 

[jime17]

hi tony. i've not forgotten. i just am working away all week and this isnt really the type of thing i can ask the wife to do. Now if you asked me to check how to spend loads of money on clothes, shes your woman.
As soon as i am back and able to do so, I will run those checks.

thanks again for your time thus far.

Jim

 

[jime17]

Hi Tony,

I lifted the top cover from the pcb. I couldnt get 1 screw ouy as it would mean removing the pump.

I cannot see any led's on the pcb. its dark in there, but nothing lights at all. not when the heating is on or when calling for dhw.

Jim.