Air block in hot water system

I’ve got some majorly bad air blocks in my hot water system.

The hot water tap in the utility room is worst affected and only a dribble comes out. There is a downstairs toilet and the hot water flow in the tap in there is fine (no kitchen yet – to follow with extension). There is a bathroom with taps on sink and bath and separate pumped shower upstairs. Flow in both those taps is fine (though it was bad for a while). Shower was fine, but has now dropped since I emptied the system yesterday.

There is a washing machine and dishwasher fed off the hot water feed that runs to the hot water tap in the utility room. This feed is half inch though I’ve been told it should have been ¾ inch to avoid a drop in pressure when appliances are on (if they did need hot water), but don’t get me started on the plumber who put it in! Pressure in both the hot water feeds branching off this pipe before it gets to the utility room sink is very strong, though it drops dramatically in the hot water tap.

Last week I turned off the mains feed and disconnected the hot and cold taps under the sink in the utility room and connected a flexi hose from cold feed to hot feed. I then reopened the mains with the intention being that the mains pressure would blow the hot water back up to the overflow pipe flowing into the cold water tank in the attic, and that this would clear any air blocks.

The pressure in the hot water tap in the utility room was fine after this. However, it dropped back to a dribble after two days, so I emptied the system last night thinking no water means no air can get blocked, but no joy, and this has caused the shower pressure to drop.

Any ideas how I can fix this? Should I have the taps around the house open or closed when blowing the mains water into the hot water system? Should I have the taps open or closed when I’m refilling the system after emptying it?

Thanks

If you had enough pressure in the hot water pipes when filling them with water from the cold mains then you should have enough pressure to get rid of the outdated tank- in- the- attic- system. Even firebird , the legendary Irish boiler manufacturer(smiley) is offering them now, better late then never. Combi condensing boilers for pressurised instant hot water . See [broken link removed]
With a fully pressurised system there is no problem like air locks, as you have seen when testing with the mains water.

Thanks Heinbloed,

Unfortunately, the system was only installed 4 months ago so replacing it is not an option. I did consider a combi condensing boiler at the time, but there is a certain amount of negativity about them out there, possibly due to ignorance, and there is definitely a large amount of ignorance amongst Irish plumbers on this subject.

An engineering friend also mentioned that Dublin City Council opposed condensing combi boilers as people have no stored water that can be used during outages, and thus makes them less tolerant of outages, and also cos of possible back seepage into their system. I was also not sure if we have sufficient pressure to go with a condesing combi, and was also told that you cannot go with a pumped shower if you are using one, which is a must for us.

I then considered a normal condensing gas boiler, but my plumber literally asked 'why the hell would you do that, it costs way more and you get nothing for it?'. I explained the long term savings to him but it was lost on him, and in the end I went with a normal system gas boiler as it was the least likely to cause hassle. Oh yeh, the guy in Chadwicks actually laughed at the idea, saying 'yeh we do them, but its gonna cost ya, like almost double the price'. I was under time constraints so couldn't put in the hours of research which this approach seems to require.