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It sounds like it has been mis-wired. The circulator pump should run all the time the boiler is on and should continue to run when heat is called for so it circulates the water in the radiators as it cools. There is normally an electronic valve that shuts flow to the radiators when only hot water is needed. Call for heat and that valve opens. It sounds like you need a mature, old school boiler / central heating technician who has lots of real world experience with older boilers. https://www.youtube.com/@MiHeatingGuy
If you have a large screwdriver, you can use it against the pump as a stethoscope to listen for the pump running. The noise is very distinctive.
Don't know your specific unit, but in general, heating systems are two-stage devices:
1: Its too cold: the motorised HW/CH valve moved to the required position, and on achieving it, the circulaion pump starts and the boiler is enabled. (The circ pump may start immediately - its not usually important.) The hot water from the boiler circulates through the heat exchanger and/or radiators until the thermostat thinks its target is warm enough, whereupon it disables the boiler, stops the pump and closes/relaxes the valve(s).
2: The boiler is off while disabled. When enabled, it heats the circulating water to a 'high' temperature and seeks to keep it there. If it reaches that temperature, the boiler will cycle on and off as necessary to maintain the set 'high' temperature. (The circulation pump must run all the time the boiler is enabled.) This may be what you're noticing. Additionally, some boilers will run the circulation pump for a little while after being disabled to reduce the temperature if the water in the pipes and boiler.
Your question doesn't say how the pump running corresponds to thee thermostat settings, but if it were stuck on, I think you'd know!
There are many ways for a hot water boiler to be controlled. One of them is to have an 'on-board' aqua-stat that cycles the boiler burners to maintain water temp set-point and the space thermostat controls only the circulating pump. There is no way of knowing if yours is set up this way, but try turning the thermostat on and off and see if the circulating pump cycles with it.
Volumns can be written on boiler control but with the limited information provided we can only guess.
You may have a carbon build up on the ignition probes but this will normally cause a lock out. It may be that the circulating pump is faulty. Ie boiler fires up but due to no circulation it shuts down on the boiler stat and as the heat remains in the boiler it will not fire again until the heat has dissapated. Changing a circulating pp can be done by a confident DIYer but remember due to new legislation the old three speed pps are no longer available. You will need to purchase a modulating pump to match you existing pump. Old and new pump threads and spacing a are the same.
how did you hot wire it. did you jump the wires on the relay board or use another power source? Does the boiler burner start? Have 120 volts incoming to the relay board? You hear relay click when turning power on/off? If so bad relay, or loose wiring terminals on the board. This control has built in transformer that can burn out, that will stop the pump relay contacts from working.
There should be a control called an aquastat that regulates the temperature of the boiler. The thermostat will turn on the circulator to start the flow of water through the radiators. If the water coming back from the radiators is very cold, a control will shut off the circulator until the boiler can come up to a predetermined temperature then start the flow of water again. If you have a tankless coil for domestic hot water, you now have a triple aquastat that maintains the temperature for domestic as well as the boiler temp. So yes the boiler thermostat (aquastat) does control the heat of the radiators and domestic hot water. No the pump is regulated by your house thermostat. You should take an amp draw on the boiler and componants to find out what is drawing more electricity than it should and popping your fuse.
hi sounds as though the system is sludged up & needs power flushing.the reason is that the water cannot circulate so over heats & pumps into the header tank.
expect to pay approx 350 400 pounds to have it properly cleansed, it will restore the system efficiency.
The other area worth considering is that it could be a faulty pump os that when th eboiler fires it cannot circulate so in turn expands & vents into the tank.
My advise is to arrange for a corgi engineer to sort it out for you.
What is the temp at the boiler? there is a temp/ presure guage it should read 160-180F. If that is OK then check the circulating pump. When the thermostat is turned up you should hear a little water moving through the piping as you have adjusted the system. If you hear nithing circulating you may have a defective pump.
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