Hot water boiler will not ignite

Call for Service. The timer is fine, the boiler has failed. I presume it is gas fired, which means that only gas registered service techs can work on it.

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!

If this is in a RV the propane monitoring valve may require more gas flow to turn on than the water heater requires. A central heating system requires substantial gas flow so when the monitoring valve opens to fire the central heating, there is enough gas flow to also fire the water heater.

This is both a complex and dangerous system. There are many factors which can cause this. I will need more information. I will ask some basic questions... Was the thermostat changed out with the a/c unit or does it have a separate one? Did the gas valve get shut off? Did the breaker get shut off? Is the water on? They have low water lockouts. 99% of the time, it is where work was done. Did they hook up the stat correctly and establish the proper type of heat on the stat? Is the circulation pump on? Is the flame control board reset tripped? Leave feedback and we can go from there.

Tell us more: What is the Solid Fuel?-- Coal?-- Wood? Is this a Steam boiler?- or a Hot water boiler?-- It sounds like Hot water, for you mention a pump-- Perhaps it is a Hot Water Circulation pump?
Does the Boiler have a sight glass?-- What is the water level?
Tell us more, so we can help you figure things out.
Mack B.

back boiler run from a gas fire? check the instructions to operate the gas heat to the back boiler not just the fire
I presume that this a fully pumped system - air lock doubtful There maybe on/off valves on the pipes to and from the back boiler [situate close to cylinder] make sure they are on - anticlockwise turn
or there could be a blockage in the outlet from header tank usually in the loft. or If there is no water in it maybe the mains cold feed it is off.
Note if no water in it DO NOT USE the back boiler

you could have a flow problem due to sludge or scale in the boiler, it could be a pump problem as it may not be circulating enough water around the system. or it could be a faulty thermostat if it is not cutting out soon enough.
1st try turning the boiler stat down to its minimum, if it still over heats then it is probably the stat.
if you have a switch on your pump to increase the speed make sure it is on setting 3. if the pump is old then it may be time for a replacement.

thats because the rinnai does not have a set up for a circulating pump it would make the unit run all the time,, they are not designed to work that way,, you will have to just wait for the hot water to get to the faucet just like before,,don't let any one tell you there is a way once the water flows it turn on the tankless so it would never shut off, you could get on that goes on a timer on say the farthest fauset away from the unit and set the timer to come on like 2 min before you are ready to use the water in that bathroom in the morning or at night other then that there is nothing else you can do

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.

Kindly

Richie

i think you will find that instead of modulating as demand requires the boiler is overheating and then re operating after the safety thermostat has operated.
i wilud put some de scaler into the main heat exchanger circuit or add it to the radiators and let it circulate for a while.
also make sure the pump is operating properly to ensure proper water flow.