Hi All,
First post here, so please be kind!
I am currently having a lot of trouble with air and related noise in my open vented heating system. Long story, with lots of things tried already, so please bear with me…
Firstly, a photo of the heart of the system in the garage as it is today (lots of spare cable length to allow me to move bits!):https://i.*********/FPl6NRA.jpg
The system originates from 1970, fully pumped, 9 radiators, 1 towel rail and a vented indirect DHW cylinder. Two-storey house, gas boiler, pump, zone valves in the garage, header tank in the loft. I changed all the radiators about 3 years ago and installed a Honeywell Evohome system with TRVs on every rad plus hot water control kit and an automatic bypass valve I added when I added the TRVs. The system was Y-plan at this time. Worked fine, no air problems ever, drained and filled fine for the radiator replacements, but the 35 year-old boiler always kettled badly. Always dosed with inhibitor. All plumbed in soldered copper, suspended floors throughout, so pipes not buried in screed.
Recently, the boiler was changed – system flushed, new Intergas HRE OV condensing boiler, Magneclean Pro2 on return, new Grundfos UPS2 15-50/60 pump on flow, taller towel rail, new header tank in loft (only ’cos the old one didn’t have a lid!), converted to s-plan (but heating zone valve locked open as Evohome does the zoning – recommended ‘figure 4’ solution from Honeywell). The other thing that was changed at this time was that the 'Registered Professional Gas Engineer' installer converted to ‘combined feed and vent’ (single 22mm to bottom of header tank, tee’d in just before the pump on the boiler primary flow, flow/return done correctly at boiler). System is dosed with Sentinel X100 and tested to be the correct strength. The filter is always very clean.
The header tank is (and always was) approximately 4.5m above the pump, and 1.7m above the top of the new towel rail, which is the highest part of the system.
Ever since this, I have not been able to get all air out of the system (or is it getting in?). The radiators make a terrible noise (sounds like ball bearings or gravel being fired through the TRV’s) which I am sure is air or gas bubbles. This is worst first thing in the morning, or when only 1 or 2 radiators are calling for heat. I have bled it literally tens of times bottom-up (all rads, pump, DHW cylinder, filter), the gas doesn’t burn or smell, so I am confident not a chemical/corrosion problem. Level in header tank is fine (always above outlet, always below overflow).
Things that have been tried (in chronological order):
1. Pump has been tried on all 3 speeds (it actually circulates fine even down at 1). No improvement.
2. I noted that the primary flow actually went slightly downhill before joining the vent pipe to the loft, so the installers (who are very helpful) returned, installed a Tower air separator (type without separate cold feed) and re-routed the pipe to run uphill. No improvement.
3. I installed a Spirovent RV2 air eliminator on the inlet to the pump. No apparent improvement, even though it was definitely ejecting air!
4. I isolated the flow at the pump valves and return at the filter, then connected a hose pipe to the drain point at the bottom of the boiler. I watched in the tank in the loft while somebody else turned the hose on – there was a huge belch of air into the header tank, suggesting that it was trapping in the feed/vent at some point. No improvement.
5. Based on point 4 above, I traced the feed/vent and found that there were significant unavoidable horizontal runs (crossing floor joists) and dips in it, so possible air locks/traps. I therefore moved the header tank in the loft, and made a new route for a new 22mm feed/vent, with significant uphill slope all the way to the loft. Guess what? No improvement.
6. I ran a separate 15mm cold feed from the loft, converted the 22mm to a vent over the tank (bend 450mm above water level), tee’d in just after the Tower separator in the boiler flow, before pump inlet (to replicate the layout of the version with the cold feed). In other words, back to a properly piped separate cold feed/vent. I.e. Boiler Flow->Tower Separator (with Vent Pipe)->Cold feed->Pump. Both pipes have nice constant fall from loft to boiler, system fills easily, no pumping over. No improvement.
7. I changed the pump valves, in case of air leak around the spindle on inlet side. No improvement.
So this is where I am today, with no improvement! As I understand, the neutral point is at the cold feed connection (approx. 0.42bar or 4.2m water), so the only section that could be under negative pressure and could conceivably admit air at any point is the short run of pipe (all soldered connections) down to the pump inlet. Is that correct?
The installers want to convert to a pressurised system, but I am very reluctant due to the nearly 50 year old pipes under floors and I sense that it would mask the problem, not cure it. I would really like to understand the problem.
Is there anything wrong with the current vent/feed/pump layout?
Could the pump itself be sucking in air?
The only very minor point in the piping design I know about is that all heating returns tee into the return line after the DHW return, but I don’t think this relates to my air troubles at all, and I get no reverse circulation in the summer.
Sorry for the very long post, but I wanted to put as many details of the steps taken to date as possible.
I would be extremely grateful for any thoughts you have.
The Pook
