biasi 24s overheating

[Agile]

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 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.

Yes, I agree that its is possible to remove the switch without removing the gas valve but its very fiddly.

Even more fiddly to replace the clip ( unless you have thin forceps.

However, you said there was condensation in the switch case. This will be because the gland is leaking! Thats virtually impossible to replace without removing the gas valve. In extreme cases the damp in the switch will create a HW demand signal!

The pin travel which I asked you to check can be checked at the left of the diverter after removing the diaphragm unit.

Tony

 

[joe-90]

Stop encouraging him to remove gas parts.

 

[karry]

how long after firing up should the HE stay cold?

 

[Agile]

About an hour!

 

[karry]

Re: DHW switch removal
Initially I was going to take of the Diverter Valve to check it but realized it has too many bits attached to it - some pipes, DHW HE, etc so opted for the back door method - it was painful but having small hands was a help.

When screwing down the glass cover, i noticed a small crack near the screw hole - I dont know whether I caused it or if it was there in the first place which could be the cause for dampness / condensation in the switch.

Also when I completely d/c the switch from the valve- continuity readings were OL / 000 i.e (open and closed) as normal. But when the switch was re-connected, I could not get (ooo) but reading showed some resistance -
I don't know if this means anything.

Re: Heat Exchanger Finns
Ok - I will check and Post

 

[Agile]

However, you said there was condensation in the switch case. This will be because the gland is leaking! Thats virtually impossible to replace without removing the gas valve*. In extreme cases the damp in the switch will create a HW demand signal!

Tony

* Although one forum person removed the entire diverter valve to replace the gland.

I dont think you have understood me! The pin gland for the DHW demand switch is leaking ! Hence the condensaton.

When measuring switches you need to measure the actual resistance which should be less than 1.0 ohm.

Tony

 

[karry]

Good Morning Agile - I do understand about the pin gland - Would mean replacing seal around the pin coming out of the valve - Thank you for clarifying.

What I meant was that maybe the condensation was from other sources than the valve because crack on glass cover.

Latest - The Plate HE overheats within minutes from cold!

I cooled the HE down with damp cloth after boiler had been on around 30 mins so it was barely warm.
I fired the boiler up again and HE overheated within 30 seconds with kettling noises.

I have checked the HW side of DV and it seem ok because the pin was going in and out fairly smoothly.Also the pin seemed to be coming out fully as well as it came oame out rather a long way.

What would render a HE plate useless other than a blockage?

 

[Homesafe]

Does you plate hex heat up withhout you opening a tap?

 

[karry]

we are talking about the main heat exchanger which does heat up without openiing a tap but only when ch mode.

The burner shuts of with temp gauge showing only 75sh (which takes 30 seconds) but the pipe is too hot to touch and the HE makes kettling noises. it

 

[Homesafe]

Latest - The Plate HE overheats within minutes from cold!

I cooled the HE down with damp cloth after boiler had been on around 30 mins so it was barely warm.
I fired the boiler up again and HE overheated within 30 seconds with kettling noises.

shirley thats plate your referring to, aint it??

 

[karry]

shirley thats plate your referring to, aint it??


I mean the HE plate for central heating circuit.

Central heating set to FULL demand
Boiler fires up and at around 75 degrees, burner shuts down.
Boiler does NOT lock out or anything. 2-3 minute pause - temp down to 60
Fires up again for 35 seconds or so -at 75 deg, burner shuts down.

Surely burner should carry on unless temp exceeds 90

 

[Agile]

NO!

The max position of the control knob is meant to be about 82° C.

Tony

 

[Homesafe]

Your problem is more than likely diverter stuck in dhw

 

[karry]

I have already check DV - the pin for DHW switch moves in/out ok

when set to HW mode only - fires up as soon as demand for water & goes off as soon as tap closed

When set to ch/hw mode - fires up as soon as CH timer demands heat =reaches 75 degrees within 30 secs - goes off - comes on as soon as tap turned on

Should it not take longer than 30 secs to reach max temp?

Bled and re-bled all rads - water gushes out albeit with bubbles

 

[Homesafe]

Check your iso valves not turned off