Before I send this to our Gas system people i want to get my thoughts straight.
We are having problems with a very noisy pump - That's one problem, but not the main one.
We have a Solar iBoost that heats up the hot water during the day using the excess electricity generated by our solar panels. https://www.marlec.co.
This heats the water to hotter than the CH/HW thermostat is set at. At 16:30 the timer for the hot water comes on, and the pump starts pumping, but I don't notice the boiler firing up. I think it must be accepted that the valve to the HW tank opens for the pump to start. It has now (17:22) been running for 52 minutes, and the pipe is warm, but not hot as if the boiler had heated the water.
2 questions:
1. Why does it start if the water is already up to temperature?
2. Why doesn't it stop because the water is up to temperature?
It is as if the controller says do it because it is time, but ignore the thermostat, even though the boiler doesn't fire because the water in the pipes is hot enough for it's sensors to say I don't need to heat water. This is an assumption that the CH boiler only fires up when the water in the pipes falls to a certain temp.
Maybe I have a failed HW tank thermostat?
Interesting at 17:37 the boiler is firing. But why because the iBoost says the water is hot? It has pumped in 2.38Kw today.
Next test, Turned down the thermostat on the HW tank until I heard it click (~50 deg) and everything stopped.
Just put it back to 65 and waiting... valve opened, pump started, so I guess the thermostat is OK.
Conclusion, Perhaps today Solar didn't heat up the hot water enough. More tests needed.
Solar circuit is independent of gas CH. It just heats the electric immersion heater, and gas CH drives hot water through a coil in the tank. Thermostat doesn't care how water gets hot.
When I adjusted the thermostat and pump started again, the boiler didn't seem to fire up unless I missed it.
Another hypothesis. The reason that the pump keeps pumping for so long is the same as the fact that it is noisy- It is faulty and not working as efficiently as it should be.
This is the way that it operates:
Timer enables Hot Water system at specified time
If Cylinder Temp above thermostat setting, no action
If Cylinder Temp Below thermostat setting, thermostat switch closes
Valve opens
Pump starts,
Boiler fires up, if Boiler thermostat below max shutoff temp.
When cylinder temp reaches set point, Switch opens, boiler stops, Pump stops, Valve closes
or
When Timer ends, Boiler stops, Pump stops, Valve ?
Ben's theory
Timer enables Hot Water system at specified time
Valve opens
Pump starts,
If Cylinder Temp below thermostat setting, thermostat switch closes
Boiler fires up, if Boiler thermostat below max shutoff temp.
When cylinder temp reaches set point, Switch opens, boiler stops, Pump keeps pumping, valve stays open.
MArch 2023
I was told that the pump keeps running for 15 minutes after the heating shuts down.
Current situation is that the bottom of some radiators is cooler than the top. Generally this is an indication of sludge buildup. My new infrared sensor shows a variation of between 2 and 10 degrees for different radiators. The radiators had been balanced in the past, but two had been turned off. Pure Gas advised me to cut off the input to the reservoir and measure it to see if there was any drop in water level indicating a leak. This was done Sunday morning, and there was no evidence of a leak Sunday night, so we left it cut off and will check again in a few days.
All the radiators have been opened fully and the house is now warmer. The ironing room and Madeleine's bedroom have been turned down.
