We've had a Ravenheat Combi for a few years and we've had quite a lot of problems with it. Is it all because there is no room stat or automatic by-pass valve?
Its only a small system with 4 radiators, each with a thermostatic valve, and no room thermostat. We've had two new pumps, a new expansion tank, new three-way shunt valve, all the TRVs sticking, banging noises quite often, various leaks inside the boiler, and the system has always lost pressure and needed topping up every week or two (when heating on). Various plumbers have repaired the boiler, but the sticking valves, noise and loss of pressure have remained a constant problem.
I'v just found an article at www.heatinghelp.com/newsletter.cfm?Id=152 which sounds like it might explain our problem. Although that system was a much bigger installation, it seems to me that the cause of the problem could be the similar - but possibly worse in our case. When the timer puts our heating on but all the TRVs are closed because the weather is mild, there is no automatic by-pass valve to allow circulation. The Ravenheat manual gives the following "general guidance": "The flow through the heat exchanger must exceed 650 l/hr when the burner is firing. It is important to ensure that this rate is achieved when sections of the system are shut off either manually or automatically. THEREFORE A BY-PASS MUST BE FITTED (shows a valve between the heating supply and return) If the circulation is too low, the boiler water temperature will rise too rapidly (which) could cause noise ... or the safety thermostat to trip". I assume that the boiler doesn't have any sort of internal by-pass a) because its not shown in the functional diagrams and b) because they stress the need to fit one externally.
What the installers did fit is a manual by-pass valve, which might be of some use during maintenance, but is no good at all when the TRVs operate in normal use.
Seems to me that when the TRVs are closed the boiler temp is rising too fast causing the noise and air venting. The pressure is rising too high and blowing the relief valve which in turn causes the system to lose pressure so that I have to keep topping it up to above 1 bar. The frequent excessive pressure is causing the leaks in the boiler and caused the pumps, expansion tank, and shunt valve to fail. And on top of all this, the frequent feed of fresh water (in our hard water area) will have caused everything to badly scale-up, and caused the TRVs to stick shut creating a vicious circle!
But I'm no expert
Am I likely right here or have I overlooked something?
- and is it dangerous?
Its only a small system with 4 radiators, each with a thermostatic valve, and no room thermostat. We've had two new pumps, a new expansion tank, new three-way shunt valve, all the TRVs sticking, banging noises quite often, various leaks inside the boiler, and the system has always lost pressure and needed topping up every week or two (when heating on). Various plumbers have repaired the boiler, but the sticking valves, noise and loss of pressure have remained a constant problem.
I'v just found an article at www.heatinghelp.com/newsletter.cfm?Id=152 which sounds like it might explain our problem. Although that system was a much bigger installation, it seems to me that the cause of the problem could be the similar - but possibly worse in our case. When the timer puts our heating on but all the TRVs are closed because the weather is mild, there is no automatic by-pass valve to allow circulation. The Ravenheat manual gives the following "general guidance": "The flow through the heat exchanger must exceed 650 l/hr when the burner is firing. It is important to ensure that this rate is achieved when sections of the system are shut off either manually or automatically. THEREFORE A BY-PASS MUST BE FITTED (shows a valve between the heating supply and return) If the circulation is too low, the boiler water temperature will rise too rapidly (which) could cause noise ... or the safety thermostat to trip". I assume that the boiler doesn't have any sort of internal by-pass a) because its not shown in the functional diagrams and b) because they stress the need to fit one externally.
What the installers did fit is a manual by-pass valve, which might be of some use during maintenance, but is no good at all when the TRVs operate in normal use.
Seems to me that when the TRVs are closed the boiler temp is rising too fast causing the noise and air venting. The pressure is rising too high and blowing the relief valve which in turn causes the system to lose pressure so that I have to keep topping it up to above 1 bar. The frequent excessive pressure is causing the leaks in the boiler and caused the pumps, expansion tank, and shunt valve to fail. And on top of all this, the frequent feed of fresh water (in our hard water area) will have caused everything to badly scale-up, and caused the TRVs to stick shut creating a vicious circle!
But I'm no expert
Am I likely right here or have I overlooked something?
- and is it dangerous?