potterton suprima 40 / 50 boiler banging weezing

Hi, recently my boiler (not sure if 40 or 50) has started to make banging and weezing noises after running for quite awhile. I have checked the pump and it is running fine with the mid range speed selected and all radiators hot. suspected the boiler thermostat (upper of the two on the boiler outlet pipe, i think?). I removed the thermistor and substituted it with the temp probe from multimeter. When the temp indicated 82 Deg C, the weezing started followed by slight banging, i switched off boiler at main switch and noticed the temp continue to rise to 97 Deg C. With the probe still in place, i positioned the thermistor so it was touching the outlet pipe and started boiler again. With the boiler thermostat at lowest setting, boiler shut down at 78 Deg C, no banging. With probe and thermistor in same position i moved thermostat away from min setting and started boiler again, this time temp rose to 84 Deg C followed by banging. So it seems that with the boiler thermostat at any position that min, the temp rosed quite high and the banging started. Is this a faulty thermistor or, sludge in bottom of Heat Exchanger. If the latter is it ok to use DS4 (seen mentioned on forum) for my open circuit system of 12 years old and how much do i use for a 12 rad system? I replaced the CB 2 1/2 years ago but now can't find anything to indicate whether it is a 40/50 or other!.

Many thanks

you really need a RGI as you have compromised the case seal and it needs checking/testing to make sure the boiler is safe to use when all is re-assembled. You should have transfered all the info to the new data badge from the old one

If the latter is it ok to use DS4 (seen mentioned on forum)

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DS 40 and the dosing rate is on the tub

twgas said:

you really need a RGI as you have compromised the case seal and it needs checking/testing to make sure the boiler is safe to use when all is re-assembled. You should have transfered all the info to the new data badge from the old one

Click to expand...

Mick, thanks for quick reply. By RGI i take it you mean an engineer! However, not sure what seal i have compromised as the thermistor just pushes into a hole on this model with no disconnections required. Or, is there something else i'm not aware of?

Kevplumb, thanks for quick reply also. As you have indicated i need ds40, i'm assuming the information i passed on from the tests have confirmed that it is sludge?

Keith

there is a seal on the front panel that you are obviously not aware of!
and I know where the sensor is

Thanks for info mick. The seal you mentioned must have been discarded by previous house owner or engineed as i gave the LH front cover a wipe over prior to re-fitting it and i could not see a seal attached. However, i will now look into it.

Back to my previous. The temp ranges indicated on multimeter when the banging started and the fact that as soon as the thermostat is moved from min position the banging starts (temp approx 84 Deg C), would you say that the thermister is U/S and the HE requires de-scaling or, just one of these requires attention

If your missing the seal then i would stop using the boiler!!!!

It's white and is attached to the case not the boiler and runs all around the outside......doh