Boiler intermittently turning on and off ? problem or normal

[koups]

HI, I don't know if this is a problem but I thought I would ask some advice.

We have a Worcester boiler connected to a Megaflow pressurised system. The water return for the radiators and hot water are connected to 2 separate flow valves and then after the flow valves the pipe joins to enter the boiler. We have a sunvic electronic thermostat that controls whether the boiler starts - we want to replace this with a honeywell evohome if possible.

I noticed that when I put the temperature down on the thermostat, the heating stops and doesn't come on- so this is working fine no problems.

However, when I put the temperature right up, the boiler does start running but it runs for about 30 seconds then stops for 20 seconds then runs again. It does this continuously. The radiators get hot OK. I just wondered if the boiler is meant to work in a pulsing manner rather than continuously? Maybe it is a way to be economical with gas??

Thanks in advance.

 

[woodsy]

Not the correct way to run if your timings are correct and not economical in terms of gas usage and boiler / component life. As to regards, the reason for it, it could be multiple reasons from system design to sludge to failing components. The best course of action would be to get gas / heating engineer in to check it over.

 

[koups]

Thanks for the reply. It seemed odd that it was cycling on and off. We did ask the Worcester chap when he was servicing the boiler and he said it was fine and that was the way it is supposed to work.

I am not a boiler expert and am not sure how the boiler works out that the return water is not enough to stop heating but I presume that it does this somehow. I would have thought that it would run until the return water is to a required temperature then stop. However, if you then switch a radiator on that was previously cold, the flow back to the boiler needs to be running so that it will notice the temperature has dropped. I have tried to work out how this works in practice but cannot work it out!

I am also not sure what our zone valves are doing and if they are working.

Sorry, these much be dim questions but I wanted to get as much information before I call a plumber so I get the right answer.

 

[jtsplumbing]

How old is boiler ? may be a circulation problem, weak pump, dirty system, Manufactures engineers tend not to be to interested in what system is doing as far as they are concerned the boiler is working, better off getting someone in to check system

 

[koups]

Boiler is about 10 years old but we have had it serviced each year by Worcester who have replaced quite a lot of parts- expansion vessel, pump and a number of leaky parts.

You are right that they probably say it is fine but to me it seems a little odd. What I dont know is how boilers tend to normally work. I guess they heat until the water is hot (not sure what water temperature would determine the boiler turning off- maybe the control dial on the front determines this from settings 1-4 where 4 is max) then switch off. I know it does the turning on/off intermittently when the water is hot. So I assumed that it was sensing a slight drop in temp then heating, then stopping again quite quickly.

I need to check if it runs continuously from cold I guess as it shouldnt turn on and off in that situation.

I have noticed that my zone valves appear to be dead so I think it would be worth replacing these- they seem to be wired through the thermostat..

 

[jtsplumbing]

When you say zone valves do you mean the 2 x 2 port valves controlling heating & hot water ? these usely go into a wiring centre and are controlled by room stat & cylinder stat

 

[koups]

When you say zone valves do you mean the 2 x 2 port valves controlling heating & hot water ? these usely go into a wiring centre and are controlled by room stat & cylinder stat

2 silver Honeywell boxes one on flow to heating and one to hot water. I am not sure they are working to be honest.

 

[jtsplumbing]

Small leaver on box, this will go floppy when valve is open,

 

[koups]

Small leaver on box, this will go floppy when valve is open,

Hmm. Very helpful. Thanks. Don't think they are working as that lever near auto and doesn't seem to move. One more question if I may. If the zone valves are not working would that cause boiler problems? Not sure what symptoms them not working would give.

Thanks so much for your help.

 

[koups]

Small leaver on box, this will go floppy when valve is open,

I think they may be broken as the leaver is just floppy and closer to the auto side- it doesnt really move either when heating running. So I wonder if this might be the cause of some boiler problems- not sure what symptoms a broken flow valve would give?

p.s. also- have tested the boiler from cold with cold radiators. Seems to run continuously so the intermittent problem only appears when the return is hot enough.

Thanks so much for your help...it has helped my understanding of what is going on!