hello everyone
I have been struggling with this combi since I moved into the flat. first, the shower would periodically go cold due to boiler cycling. the lower the mains pressure, the more often/likely it will go off and then on. very annoying. I "fixed" the problem by buying a shower head with a better throughput. with the new head it would only cycle if the shower was set too weak/cold or the mains pressure was too low.
recently I started renovating the bathroom and installed a thermostatic valve with divertor (hudson reed). with the valve in place, boiler keeps cycling and although the thermostatic valve does its best (?), the temperature fluctuates a bit, around 1.5C colder shortly after boiler has cut off.
today I did some experiments on the whole setup. with the kitchen tap fully open on hot -- no cycling. temperature ~60C. with shower AND kitchen tap running -- no cycling. cycling only starts when I consume less hot water. I made some measurements and from the shower hose, with thermostatic valve set to 37C, an 11-litre bucket gets filled with 64 seconds, no cycling. with a good shower head, in 78 seconds, cycling.
AFAICS, with figures like that I cannot be suffering from a low mains pressure. it looks like my boiler needs good flow of hot water in order not to cycle.
the boiler spec says that the domestic water production at delta 30C is
14.3liters per minute and 12.3 liters per minute for delta 35C. it doesn't specify the minimum flow required. what is also interesing, is that the boiler's panel has a knob for adjusting the DHW temperature. when I turn it to minimum, the hot DHW output from kitchen tap is 62C, on maximum it is 66C (both for high flow). not that much of a difference. also, I don't see flame modulating at all (through a window). I measured hot only from a kitchen tap and got the following data: 11l bucket in 1:47 (no cycling), the same bucket with lower flow in 2:50, no cycling but the temperature was 78C (!!!).so now I am completely puzzled, whether the boiler is operating incorrectly, or my installation is incorrect. but recalling that I always had problems with DHW temperature, I am not sure about the latter. to get sensible temperature from a kitchen tap I have to open it to full, which is very difficult to use, water splashes all over the place. if I reduce the flow, boiler starts cycling.
I looked at the valve, and despite 1/2" and 3/4" sizes used everywhere, on the divertor I can see that the holes are ~5mm in diameter. surely this restricts the flow.
could it be that my mains pressure is too high and I need to fit a pressure reducing valve?
my setup is as follows:
boiler: ferroli modena 102, 30KW pipework: 15mm copper, thermostatic valve ~5m from the stopcock, the same distance to the boiler.
I would be extremely helpful for any advice or analysis. I'd like to diagnose the problem myself and only then call for a boiler specialist once the boiler is identified as a culprit. maybe I could take some additional steps to increase the flow through the hot circuit? or reduce the cold pressure?
my suspicion is that the boiler is running too hot, doesn't modulate and the lower the flow, the higher the temperature. the shower valve might be reducing the hot flow to get the temperature right, therefore boiler cuts out.
thanks very much for reading.
/max