I have a vokera compact he35 combi and would like to check a few things:
1. Is the DHW thermostat “dry” or does the boiler need to be drained to replace this?
I ask the above as I am experiencing a few issues with the boiler and thought of trying the above first.
Hot water is running hot and cold (cycling) if the thermostat on the hot water is turned too high. Boiler overheats, turns off, water goes cold, system cools, fires up again and heats and so on. If I turn it down I get a constant hot water supply (currently set to 45-deg C as measured at the sink using a IR thermometer) and boiler fires continuously. Turning the DHW temp to max causes much more rapid on/off of the boiler and corresponding hot/cold cycling at the hot water tap.
Another strange observation is the main CENTRAL HEATING FLOW pipe gets hot at the same rate as the hot water pipe, even when heating is off, indicating diverter valve issue. This happens even if the DHW is set to 45-degrees and I get a constant steady stream of hot water and boiler continues to fire. Whilst the copper CH FLOW pipe gets hot (1st metre before it runs under the floor so I can feel it) I have not detected any heating of the radiator that is first in the CH loop (another 6ft away from the boiler). Its definitely not heating the flow pipe by conduction and I am definitely getting hot water flow into the CH pipe when HOT WATER is called for, so the diverter is letting WATER pass. The same is not true in reverse, i.e., the DHW pipe does not get hot when the heating is on.
My initial thoughts on cycling at the hot tap
- Secondary water heat exchanger blocked, BUT no limescale issue in Glasgow and flow rate and pressure of hot water excellent. Possibly blocked at main CIRCUIT supply side. Unlikely as whole system only 4+ years old and completely cleaned, flushed and inhibited over summer.
- Diverter valve spool sticking – again, surprised at this as newish system and all recently cleaned, but possible. Perhaps diverter motor issue? Would faulty diverter cause thermal cycling at the hot water tap?
Pressure set at 1-bar and has held pressure all summer, so no issue there. If replacing the diverter spool or motor, would you recommend dropping who system pressure before isolating boiler and draining or should the boiler isolating valves hold 1-bar?
Curious to know your thoughts on the above and any suggestions for fault finding. Vokera technical suggested getting venture flu cleaned!
1. Is the DHW thermostat “dry” or does the boiler need to be drained to replace this?
I ask the above as I am experiencing a few issues with the boiler and thought of trying the above first.
Hot water is running hot and cold (cycling) if the thermostat on the hot water is turned too high. Boiler overheats, turns off, water goes cold, system cools, fires up again and heats and so on. If I turn it down I get a constant hot water supply (currently set to 45-deg C as measured at the sink using a IR thermometer) and boiler fires continuously. Turning the DHW temp to max causes much more rapid on/off of the boiler and corresponding hot/cold cycling at the hot water tap.
Another strange observation is the main CENTRAL HEATING FLOW pipe gets hot at the same rate as the hot water pipe, even when heating is off, indicating diverter valve issue. This happens even if the DHW is set to 45-degrees and I get a constant steady stream of hot water and boiler continues to fire. Whilst the copper CH FLOW pipe gets hot (1st metre before it runs under the floor so I can feel it) I have not detected any heating of the radiator that is first in the CH loop (another 6ft away from the boiler). Its definitely not heating the flow pipe by conduction and I am definitely getting hot water flow into the CH pipe when HOT WATER is called for, so the diverter is letting WATER pass. The same is not true in reverse, i.e., the DHW pipe does not get hot when the heating is on.
My initial thoughts on cycling at the hot tap
- Secondary water heat exchanger blocked, BUT no limescale issue in Glasgow and flow rate and pressure of hot water excellent. Possibly blocked at main CIRCUIT supply side. Unlikely as whole system only 4+ years old and completely cleaned, flushed and inhibited over summer.
- Diverter valve spool sticking – again, surprised at this as newish system and all recently cleaned, but possible. Perhaps diverter motor issue? Would faulty diverter cause thermal cycling at the hot water tap?
Pressure set at 1-bar and has held pressure all summer, so no issue there. If replacing the diverter spool or motor, would you recommend dropping who system pressure before isolating boiler and draining or should the boiler isolating valves hold 1-bar?
Curious to know your thoughts on the above and any suggestions for fault finding. Vokera technical suggested getting venture flu cleaned!
