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By rikur_
FLYER Club Member  FLYER Club Member
#1886421
Bill McCarthy wrote:Pump cavitating due TRVs shutting down causing reduced flow.

I'm guessing at something along those lines - also getting a bit of kettling from the boiler which would imply the flow rate may not be high enough. I thought the ABV is supposed to compensate for the TRVs closing off, but it's adjustable so might not be correctly adjusted. There are two bypass radiators and two towel rails with no TRVs, but none are fully open to preserve the need to balance the system when cold.
Edit: Fully opening the bathroom towel rail stops the kettling so I think I have a flow issue
You shouldn’t have to drain down the system to remove a radiator - shut the TRV and the throttle valve at the other end, noting how many turns to shut

I was permanently removing a massive conservatory radiator and associated pipework hence easiest (for me at least) to drain down and refill
By Big Dex
#1886441
You may have a partial airlock in the system; I suggest closing off all radiators bar the one furthest from the boiler (with the system running, pump set to 3, ideally on heating only) with the ABV closed down. Allow that to run for a minute or 2, then open the next closest radiator (order not that critical), before closing off the first. Repeat that pattern until you've done all the rads, and return them to normal settings. This should push any residual air into the rads, where it can be bled out.
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By rikur_
FLYER Club Member  FLYER Club Member
#1886456
Big Dex wrote:You may have a partial airlock in the system; I suggest closing off all radiators bar the one furthest from the boiler (with the system running, pump set to 3, ideally on heating only) with the ABV closed down. Allow that to run for a minute or 2, then open the next closest radiator (order not that critical), before closing off the first. Repeat that pattern until you've done all the rads, and return them to normal settings. This should push any residual air into the rads, where it can be bled out.

I'll give that a go. The problem airlock I've had in the past is on the 28mm return to the boiler. See schematic below, it's a first floor airing cupboard, and the pipes run under the first floor for ~30ft to the corner of the house, and then drop down a duct before going through the wall to the outside oil boiler. The problem is that the highest bit is just before it drops down to the boiler, and it won't pump the air down through the filter, condenser and boiler. Unfortunately this high spot is right above the electrical consumer unit, so I'm hesitant to put in a bleed valve. I think in this case the best option may be to open the drain valve on the mag filter to see if I can get enough flow to draw the air down. (I did fit a bottle bleed valve just above the mag filter, because otherwise the condenser was not clearing of air. )
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By Bill McCarthy
#1886460
I fitted my auto vent on a “teed in” vertical piece of 22mm pipe (300mm high ) as any bulk air bubbles would skip past a short 15mm pipe. The vertical pipe gives more useable volume for the air to enter.
You have checked your filter clear of magnetite ?
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By rikur_
FLYER Club Member  FLYER Club Member
#1886463
Bill McCarthy wrote:I fitted my auto vent on a “teed in” vertical piece of 22mm pipe (300mm high ) as any bulk air bubbles would skip past a short 15mm pipe. The vertical pipe gives more useable volume for the air to enter.
You have checked your filter clear of magnetite ?

Filter is clean.
The way my autovent is fitted at the boiler end is such that when the flow stops, any air in the condenser flows back up the return pipe to the side of a T, with the vent on top, and the circuit to the bottom. Seems to work, you sometimes get a little turbo charger style hiss just a few seconds after it all stops. (In the ideal world the pipe would rise all the way to the loft vent, but when the mag filter was fitted below the worktops it resulted in a drop through the mag filter, hence trapping air in the condenser)
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By Rob L
#1886467
Off-piste (but not off-topic), I recommend after a warm summer and before firing up a central heating (CH) boiler for the winter after a long layoff (the following only applies if said pump is used solely for CH ):

Take a few minutes and turn the water pump impeller with a screwdriver. Accumulated crud/friction etc could cause the pump to not turn, which might blow a fuse or even worse, blow the pump. Mine is a Grundfoss (or knock-off), but I'm sure many others are similar.
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By rikur_
FLYER Club Member  FLYER Club Member
#1888453
stevelup wrote:
What is the bypass - a carefully calibrated :lol: manual valve - or an actual ABV?

One of these
IIRC it is purely there as a protection. I think because we have 2 towel rails and 2 radiators without TRVs, there is still sufficient flow through the boiler even with all TRVs closed, and therefore in all 'normal' scenarios the ABV should remain closed .... but the ABV protects against e.g. the main actuator valves failing.

I *think* I've solved the issue by running the system with everything fully open, and the pump turned up to maximum for an afternoon. Fingers crossed.
By NigelC
#1888564
I have a 23 year old Potterton with cast iron heat exchanger which apart from occasional fan replacement, 4 screws and a lead to plug in, has been utterly reliable.
Three different gas engineers over the years have advised me to keep it as parts are available and rarely required. I calculated the monthly gas savings of changing to a condensing boiler and the savings would barely pay for the boiler within the warranty period let alone installation.
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By Boxkite
#1888595
NigelC wrote:I have a 23 year old Potterton with cast iron heat exchanger which apart from occasional fan replacement, 4 screws and a lead to plug in, has been utterly reliable.
Three different gas engineers over the years have advised me to keep it as parts are available and rarely required. I calculated the monthly gas savings of changing to a condensing boiler and the savings would barely pay for the boiler within the warranty period let alone installation.

You have a fan? That's very modern :D
I haven't upgraded my 30-year-old Ideal Stelrad (oh so simple, but has needed one new thermostat and the odd leak dealing with); the upgrade would never pay for itself. It is a bit noisy though.