Hello again all!
My boiler is on the blink again - it's a (now somewhat old) Worcester 28CDi RSF, and has previously had the DV diaphragm, fan and PCB replaced (by a competent tradesman where appropriate), as well as the manual timer replaced with a computerised one following various problems.
The current problem is that whilst CH is fine, DHW gives the correct lights and indeed (after a short delay) a supply of water at a good temperature, but pressure fluctates rapidly from 1.3-1.8 bar or so (set at 1.5 bar when cold) and after 20-30s or so there is a banging noise, lights and burner go out, water becomes cold, then shortly after that burner comes back on and the cycle starts again. Sometimes the banging occurs whilst heating continues as opposed to coinciding with it going off.
I have had the water-water heat exchanger off and checked for any blockages - seems to be clear. The pump is working, responds to speed changes (left on high for normal operation) and as noted CH is circulating OK. Hot water taps have good flow with boiler turned off.
The thread on the plastic manifold connecting water-water HE output to gas-water HE input (i.e. cold water flow) is completely shot and was leaking (very temporary fix with a thicker washer currently holding), so I've ordered a new manifold and will fit that, but it seems unlikely to be the problem.
Water has obviously previously escaped through the auto air vent on top as there is a brown patch on the ceiling above this. The cap has always been left on loosely to allow air to escape. Radiators do not release any air when bled, only brown water.
I think I have an overheating issue here, or maybe a thermistor fault - could I get a little help please? Happy with working on water parts, know not to touch gas ones, and believe this is the former at present.
My boiler is on the blink again - it's a (now somewhat old) Worcester 28CDi RSF, and has previously had the DV diaphragm, fan and PCB replaced (by a competent tradesman where appropriate), as well as the manual timer replaced with a computerised one following various problems.
The current problem is that whilst CH is fine, DHW gives the correct lights and indeed (after a short delay) a supply of water at a good temperature, but pressure fluctates rapidly from 1.3-1.8 bar or so (set at 1.5 bar when cold) and after 20-30s or so there is a banging noise, lights and burner go out, water becomes cold, then shortly after that burner comes back on and the cycle starts again. Sometimes the banging occurs whilst heating continues as opposed to coinciding with it going off.
I have had the water-water heat exchanger off and checked for any blockages - seems to be clear. The pump is working, responds to speed changes (left on high for normal operation) and as noted CH is circulating OK. Hot water taps have good flow with boiler turned off.
The thread on the plastic manifold connecting water-water HE output to gas-water HE input (i.e. cold water flow) is completely shot and was leaking (very temporary fix with a thicker washer currently holding), so I've ordered a new manifold and will fit that, but it seems unlikely to be the problem.
Water has obviously previously escaped through the auto air vent on top as there is a brown patch on the ceiling above this. The cap has always been left on loosely to allow air to escape. Radiators do not release any air when bled, only brown water.
I think I have an overheating issue here, or maybe a thermistor fault - could I get a little help please? Happy with working on water parts, know not to touch gas ones, and believe this is the former at present.