system boiling

[cathy]

we have recently upgraded an existing central heating system, and now have 16 radiators, and two seperate hot water tanks, fired by a Grant oil boiler 28-35kw. the room thermostat controls the heating system, and independent thermostats on the water tanks, which are both on independent zones.

Our problem is that the system boils from time to time. It seems to boil regularly when the far water tank is on, and the water temperature constantly far exceeds that on the thermostat.
when the heating to this water tank is turned off it still boils in the inflow water tank to the heating system, and we think this happens when the room temperature reaches the required level - currently set at 18.5C - ie when the system is calling for complete shutdown.

As you can imagine, the system is complex, with three valves on the system, a pump, and we do not fully understand it - but we are all confused as to why the valves (or boiler) do not shut the system down when it reaches the required temperature. After about 30 secs of boiling, it does then manage to shut down.

We are sure this is not doing the system any good, and wonder if you can come up with some suggestions as to why this should be happening. Our engineer is unsure.

 

[matt666]

Hi, When you say "system boils" do you mean one of the domestic hot water tanks boils?

 

[ecowarm]

Wiring problem by the sound of it, but can not see how it would actually reach boiling point? is it just a kettling noise coming from the boiler? does the hot water actually boil? is there an immersion heater turned on with a faulty stat?

 

[Bartdude]

I agree it could be wiring.When the hot water temperature is too high,is the boiler still running??

Did your installer do the wiring or did he use an electrician?

 

[justlead1]

Hi Although my experience i dated in this area of the trade. Perhaps small pipes and know over run on the pump may be an issue. There are people on here that will advise but may be more information is needed?

 

[stevetheplumber]

possibly there is nowhere for the pump overun to pump to to when all valves shut so may ned a bypass before the valves ?

 

[cathy]

Hi, When you say "system boils" do you mean one of the domestic hot water tanks boils?

I think it is the 'feeder tank' for the central heating that is boiling. From downstairs it sounds as if there is a steam train coming along the track! The water from the external boiler to the control stats (about 30ft away) is exceedingly hot and you are unable to touch the pipes at all so they are probably boiling too. The wiring was installed by a qualified electrician, but it is a complex system. It is definitely NOT either water tank that is boiling, but as I said the far water tank at the far end of the house does get far too hot for the temp it is set at (60), so the thermostat may be faulty, but even when that tank is turned off the system still boils occasionally. It is all very confusing as we do not really know anything about it!

 

[Bartdude]

That sounds like a problem with the boiler thermostat,Grant boilers have an overheat thermostat that shuts the burner down if the main thermostat fails.Have you ever had to reset that?

The thermostat sensors may not be in their pockets on the boiler,I've seen that before.

Have you been in touch with Grant? Their technical support is usually pretty good and if the problem is with the boiler it will be fixed under warranty.

 

[cathy]

thanks for your input - we did have an electrician to do the wiring.

 

[cathy]

Thanks for your answer. we will contact Grant tomorrow to see if there is a problem with the boiler.

 

[cathy]

thanks for your reply. I will ask our installer to comment on this, but I think he has thought all of this through.

 

[cathy]

Thanks for this. Some of our pipes are small, but the majority are standard. However, I will ask the contractor to take a look at this issue. I think he has planned for the small pipes however.

 

[RoryD]

I think it is the 'feeder tank' for the central heating that is boiling. From downstairs it sounds as if there is a steam train coming along the track! The water from the external boiler to the control stats (about 30ft away) is exceedingly hot and you are unable to touch the pipes at all so they are probably boiling too. The wiring was installed by a qualified electrician, but it is a complex system. It is definitely NOT either water tank that is boiling, but as I said the far water tank at the far end of the house does get far too hot for the temp it is set at (60), so the thermostat may be faulty, but even when that tank is turned off the system still boils occasionally. It is all very confusing as we do not really know anything about it!

Not oil qualified, but if you have an immersion heater on your cylinders, you might like to ensure they are turned off. CH boiler providing hot water AND immersion heater on = an absolute tragedy when feed & expansion tank melts