biasi 24s overheating

[karry]

I have at home a Biasi 24s in an average 3 bed semi with 8 radiators,
HW works fine but I am sure it used to be bit hotter when set at max.
The pressure is set at 1bar but I have experimented by increasing to 1.5

The issue is with CH. The boiler fires for only 30 seconds after a few minutes repetitively

The flames switch off when the temp is about 75degrees but temp gauge continues to climb to 85+ before it comes down to about 60 degrees and burner fires up again.

The flames are blue and full for about 15-20 seconds and dies down to low for abut 5-10 seconds. The HE makes kettling noises.

Only a couple of rads heat up after about an hour. If left overnight the it locks out with the red-light coming on.

The flow pipe is untouchable hot while the return is cold.
It seems like its a circulation problem so I have replaced the pump (which was replaced only two years ago - replacing the original 13 year old one)

I turned off the d/s rads and the upstairs one heated up. Then I turned on d/s again but now non of them heat up despite hours of bleeding. The water coming out of the rads seems very clean, only slightly pale due to inhibitor put in last time I power flushed and drained the system 2 years ago.

The water drained from the boiler several times this week has been very clear with a few specks of soot.

I am advised by couple of Gas safe guys that system needs a power / flush. But I suspect HE due to condition of drained / bled water.

Could it be a knackered main HE or could it be just blocked with limescale?

 

[Agile]

You could check that the diverter valve is fully returning to the rest position when not providing hot water. You can do this by removing teh diaphragm unit from the body of the diverter valve. The pin travel should be about 9 mm.

Start boiler from completely cold in the CH mode and see if the plate HE immediately gets very hot!

 

[karry]

Thank you for quick reply at this time of night.

The HE does quickly overheat from cold(within a minute) - that is the problem - the burner does not stay on for long for heat to travel most rads.

I dismantled the two diaphrams - Big one for DHW and smaller one facing the front (CH) and they looked OK -

I also took the DHW flow switch off to check if the pin for the switch was siezed - ( I read on this forum that if the pin is seized in out position it could make the boiler think there was demand for HW therefore knock the heating off) but it moving in and out OK

I assumed the CH pin is OK because the burner switches on quite quickly if not instantly.

P.S. what time do you goto sleep??

 

[petertheplumber12]

If the HE was blocked with lime scale it would probably kettle, Do you have 22mm flow and return feeding the rads and dropping to 15mm on each floor, or is it 15mm all round the house. If all 15mm for rads they will struggle to heat, if 22mm then balancing is the answer probably.

 

[karry]

they are 22 for feed and return with branches of 15 to each rad.

1 what are the circs for Plate HE being beyond repair?
2. what do I use to clean the HE?
3. Could it be main circuit temp probe at fault due to fact gas is cut off at about 75-80 instead of 90 although gauge reaches 90, approx 15 secs after cut off

The lockout only occurs after hours of 30 second cycles forcing the safety TS to cut out so that seems to be working.

If all the rads heated up within reasonable time albeit poorly I would think BALANCING.

The boiler used to stay lit on max heat for 5-10 mins at a time as opposed to 30-45 seconds.

My Plan of action on weekend.
1.Remove HE and rinse it out with some chemical cleaner
2.Drain the whole circuit.
3.Swish out all Rads one by One
or
Hire a Power Flusher but reluctant to spend more cash on 15 year old boiler - Already spent £65 on pump, £55 on call out who advised a power flush, pump or a new boiler.

 

[petertheplumber12]

If you do what you have suggested then a powerflush is unnecessary. Only clean all rads IF you think sludge is present in them. eg cold at bottom hot on top. If very bad for that then you will find out when you do the first one in the garden with a hose. If really bad then after all rads cleaned a powerflush or chemical clean for a week will help clean the pipes. Test pipes with a magnet if a magnet sticks to copper then it has sludge inside it.

 

[Agile]

It seems this poster is being encouraged to do work involving gas/combustion components which is contrary to the rules of this forum!

 

[joe-90]

Err - where?

 

[Agile]

He has apparently removed the gas valve!

Now he proposes to remove the main heat exchanger!

Thats all gas/combustion related work a DIYer should not be doing!

He should be calling an engineer!

Tony

 

[onecog]

I would be looking to change the main temp probe first.
You can check out the one that's on there at the moment if you know how but for £8 i would buy this.

http://www.amazon.co.uk/Biasi-Replacement-Temperature-Thermister-BI1001117/dp/B005HBWSWK

 

[karry]

What makes you think I removed the gas valve?
If its the fact that I removed the DHW switch then please be informed that it is possible to take that off and replace it without removing the GV.

I took off the ignition module
Brushed aside the cables and made an opening so I could see the switch properly
I got a large flat screwdriver to prise the fork off. I jammed the flat blade against the glass body and and gradually prised it off.

To Refit used my thumb to push it in position while holding the switch in situ with other hand.

It was bit awkward but was done in 10-15 mins.

I took it off partly to check the pin travel but it also was a bit condensated so I opened the glass cover, dried it, tested it with a multimeter. It seemed OK so I put it back.

 

[Whitespirit66]

Start boiler from completely cold in the CH mode and see if the plate HE immediately gets very hot!

OP - Did you try Agile's advice in previous post?

After this you mentioned the hex overheating. Have you done the above and felt the DHW 'PLATE' hex to see if it gets very hot?

 

[karry]

No - I have not yet - The output pipe is too hot for touch so I assume the HE will be hot too. The flow pipe heats up beyond touch after a minute or two.
I am not at home now but I will do that test and post.

What will the temp of HE from cold indicate?

The pump (CP61) was heating up so I thought weak pump was the issue. Gas safe engineer backed this theory up so we replaced it with a new (CP63) a couple of days ago. But within 10 minutes it was as hot as the old one.

I have not checked the Bypass but quite a few of the Rads do not have TRVs anyway - would a faulty bypass valve still cause overheating?

 

[Agile]

The pump (CP61) was heating up so I thought weak pump was the issue. Gas safe engineer backed this theory up so we replaced it with a new (CP63) a couple of days ago. But within 10 minutes it was as hot as the old one.

You will notice that no one here advised you to get a new pump!

Tony

 

[Whitespirit66]

What will the temp of HE from cold indicate?

The secondary dhw plate hex should only come into use when you run a hot tap.

If you start the boiler cold on heating only, and the plate hex gets hot, then the diverter maybe faulty. If the hex stays cold, it rules out the diverter.

Untitled

• Whitespirit66
• 1 Feb 2013
• 1