sludge sysmptoms?

[hammers4spanner]

issue with a old gravity system approx twenty years old ,owner complained about noisey pipes and heating /hot water not coming on .Gone out and their is a load clanging noise coming from pipework when switch on demand for either dhw/ch ,flow pipe gets hot but no heat on return and obviously boiler gets hot then cuts out .just for note checked the 3 port and and flows out to system and hot water fine.Plenty of air came out the system from the aav in cupboard and system has not gone dry judging by f & e tank . They have also mentioned that hot water came out overflow yesterday on first issue of this happening although not seen it myself yet can feel the cold feed pipe and vent get very warm. Tank in loft seems plenty high enough and pump accordingly located to stop pumping over which makes me think a blocked return piupe with sludge??

 

[Leo21]

Has got an airjec/ air separator? These can block up, is the pump strong? And sometimes the return into the boiler gets blocked.

 

[diamondgas]

Make and model of boiler ?

Initially sounds like the pump is faulty .. especially if it has all of a sudden given symptoms IMHO

 

[diamondgas]

oh! When you say "gravity system." I'm assuming you mean 'open' yeh?

 

[ecowarm]

A DG above, not a gravity system if it has a 3 port

 

[JCplumb]

Another vote for the pump being the issue.
This same thing happened in my house before I was a plumber, my ex's cousin was a BG engineer and came out to look at it, within 2 minutes he diagnosed the pump but said he couldn't use his BG stock from the van so he told me how to change the pump.
I went to the big orange shed and got a pump and changed it myself in about 1/2 an hour, that was my 'lightbulb' moment and I enrolled in the next available plumbing course at college.
12 years(ish) down the line now and I kinda hate him

 

[SimonJohns]

I would say circulation issue too, would check pump and valves first

 

[hammers4spanner]

Make and model of boiler ?

Initially sounds like the pump is faulty .. especially if it has all of a sudden given symptoms IMHO

heat only boiler cant think of model off my head ,,,yes open vented system.

 

[diamondgas]

heat only boiler cant think of model off my head ,,,yes open vented system.

Has to be the pump H4S

Only other possibility would be serious blockage or no water in the system, feed blocked?

 

[hammers4spanner]

Dont think feed is blocked as drained water out and cold hear tank in loft filling ,,,whats your thought process of pump not working or makoi=ing that noise??

 

[SimonJohns]

Water not circulating
Water boiling in boiler
Boiling noise is banging noise
Feed gets hot through convection and conduction

 

[diamondgas]

Pump fails on a Low water content boiler, lot of initial heat and going nowhere equals localized boiling, rapid expansion up the flow pipe and out to open vent. 1st thoughts anyways

 

[hammers4spanner]

problem being the pump must be circulating as when change it dhw to ch the can feel the temp change throught the 3 port to ch ,,,and why all the sudden air in system?? sorry if coming across as a doughnut here lol

 

[diamondgas]

problem being the pump must be circulating as when change it dhw to ch the can feel the temp change throught the 3 port to ch ,,,and why all the sudden air in system?? sorry if coming across as a doughnut here lol

Basic gravity could account for change in temp potentially H4S ... rapid heating of the flow would indicate poor circulation, I'm assuming that is what is happening? If it isn't the pump, the main circulating component, then a restriction of some kind is stopping the heat being removed from the boiler. Is the flow mad hot and the return relatively cool?

 

[hammers4spanner]

Flow gets roasting hot and return stays stone cold , gets hot upto cylinder cupboard then boiler cuts out .