Temperature generated by Baxi 552 at indirect coil

[jirams]

I have been measuring the temperature (IR thermometer) at the feed side of the HWC indirect coil from 552 over several on off cycles and am puzzled. When the boiler is burning there is little increase in temp at top feed into coil - around 53 C. Then suddenly the temp shoots up to almost 80 C. for 2 or 3 minutes and then creeps down to low 50s. I don't understand why there is this sudden fast shoot up - I would have expected the temp to creep up and down steadily as the boiler burned and then switched off on boiler stat. I am getting rumbling / gurgles at some parts of the on cycle which I suspect is expansion and the expansion primary pipe cycles up to 45 c. and this is why I started this experiment with temp measurement.

Any ideas welcomed.

 

[dickyboy]

I had a similar problem last winter. We tried allsorts and it turned out to be an almost blocked cold feed and vent. We rang baxi and got correct temp settings and measured differential between flow and return temps. If the boiler is banging, that is showing a lack of water/circulation problem. I would be investigating further and looking to see how clean system is. Start by checking header tank, cf and vent and then flow and return pipes at boiler and cylinder. Could be a powerflush thats required.

 

[jirams]

I'll investigate the CW feed - have suspected this. The noise isn't actually from the boiler/heat exchanger - more in the primary pipes somewhere - is not heard in the actual attic - very hard to pinpoint exactly where - the system is probably older than most folk on this forum !!! Would not risk power flush as the rads etc would probably vanish ;0)

 

[aggis]

I presume the the circ's to the cylinder are gravity.
What temp is the cylinder return ?
Does the noise sound like a kettling noise ?
If it seems to be circulating you could add a noise reducer Fernox F2 or Sentinel x200.
If not circulating then your pipes to the cylinder could be blocked, if slight circulation could cleanse with chemicals or powerflush.
If none or very poor circulation you'll need to cut the blockage/pipes out. start by looking at cold feed if piped into cylinder return.

 

[dickyboy]

Good luck. I know what you are up against. At the end of the day if the system is that bad then the customer needs to spend some money on it and get it sorted. As the saying goes, "you cant polish a turd"

 

[jirams]

Gravity - return at cylinder sits about 10 C below feed. I'll check CW feed at cylinder for flow if I can. The noise is not IMO kettling - more like pipe rumble due to air bursts. All the rads only bleed out clean water at bleed valves.

 

[jirams]

Yeah - I should have done something about this old set up before I retired (I'm now 70 and can't do things the way I used to!!!). It has been going for 28 years !!! and has been VERY VERY reliable. In all that time the only failures were the gas solenoid 10 years ago and the spark igniter 1 year ago. My philosophy of 'if it ain't broke - don't fix it' is now biting my bum, perhaps? I am sure that the 552 system's tubes are in a better state than mine are now !!