Morning folks I'm trying to understand why 4 out of the 9 radiators in the house have failed within the space of 6 months and how to prevent it going forward. I dont know much about plumbing and the following is what I have been able to deduce from talking with folks that do and reasoning what I see ... so it may be jibberish. The boiler is located just outside the house in a dedicated boiler room - concrete shed - and from the day we purchased the house up until now (3 years on), there have been two pipes heading up into the boiler with valves on each. These valves have been open and from what I can tell, its a vented system as the exhaust coming out the back of the boiler shed will spew out steam on occasion. Im guessing that this means there has been a constant supply of water coming into the boiler, its heated up and then when it gets to a certain temperature or pressure, the boiler will vent off? Keeping the entire system at a steady pressure rating? The radiators were all installed at the same time about 10 years ago and have been systematically bursting - just little pin holes, but generally on the face of the radiator. The water inside is mostly clear although there has been one or two radiators with a brownish tinge to it. So by my reckoning, what has happened is that with it being vented and exposed to a fresh stream of water constantly, there is no rust inhibitor in the system at all by this point causing the radiators to rust from the inside out.. this, I'm guessing, means that all the radiators will essentially need replaced since they were all installed at the same time, they will all likely be on the verge of going the same way as those that have burst. Plumber came in and replaced two of them and then tinkered with the two valves leading into the boiler. The boiler activates at 0.5Bar, so I have been opening the valves and letting the pressure up a little before turning them off. The boiler maintains the pressure, the water heats up and then excess is vented. obviously this means when the heating goes off during the day, it all cools, the pressure drops below 0.5 (pretty much to 0 bar) bar and then needs me to open the valves again when we want the heating to go on. Should I be doing this? Ideally, I think the solution should be to replace the radiators, get inhibitor in there and then not have everything venting off... How do I get the balance right or what are your thoughts on where I should go from here / look into?
I'm no plumber either, but if it is an open vented system, the pressure should not be able to rise, any expansion of water is dumped into a header tank in the loft (Not the cold water tank). Can you confirm the boiler make & model, that would help. But the reality is no plumber should have thought it was okay to do this and walk away. Assuming its a fairly standard PRV it would normally go around 3 bar. I would get some more advice from here, but look for a new competent plumber in the mean time as I suspect you need one.
The PRV does open at 3 bar, im at work at the moment but I can confirm make / model when Im home. Plumber is coming back, just waiting on the other radiators to come in this week and said to see how it gets on with it not being "open" 24/7.
From what you describe - 'exhaust spewing steam', 'PRV's and the 'pressure having to be a min of 0.5 bar before it operates', this is NOT a vented system but a sealed ('unvented') one. And the pressure should NOT get to the point where it blows open the PRV. And you should NOT have to keep topping it up. The system pressure should be fairly constant - say around 1 bar when cold and ideally increasing only marginally - say up to 1.5bar when hot (although some systems seem to be happy with larger swings than this). But nowhere near 3 bar! It sounds as tho' you don't have a properly operating expansion vessel - these are the items that accommodate the expanded hot water, and then release it back in to the sealed system when it cools - ergo your pressure should stay relatively level. What make and model of boiler is it? But, yes, that would explain your rusty rads - a constant supply of fresh aerated water and no inhibitor. And, yes, the other rads will be on their way out too. Also - your system is BOUND to have a shed-load of sludge in it too from all that internal corrosion, so you should be looking at adding cleaning chemicals and a magnetic filter on the 'return' AFTER you've sorted the pressure issue. Boiler make and model?
As DA said, I reckon its the expansion vessel not operating properly or at all. With the pressure at 0.5 bar cold, pressure will increase substantially when hot unless there is somewhere for the pressure "to go". This is the job of the expansion vessel. My guess is that the expansion vessel isn't expanding at all, so the pressure increases to above 3 bar when the PRV blows, releasing hot water and reducing the pressure. When its cold pressure is low requiring you to top it up. And so the cycle repeats. Boiler make and model?
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