Hi, The hot water on our elderly Glowworm boiler is scorching hot even with the boiler thermostat set to minimum. Would the likely cause be a faulty boiler thermocouple or thermostat, or too high gas pressure? I'm sure that the water being too hot is making the CH pump to become very noisy. Constant bleeding of the (newish) pump helps for a while, but becomes noisy again several hours later. I assume both problems are connected. Regards Dave
The problem will be the primary circuit thermostat built into the boiler. This stat is important for safe operation. The HW cylinder stat will also be either faulty, set very high, fallen off, or never fitted.
Thermocouple and gas pressure have nothing to do with it. Thermocouple failure causes the gas to cut off.
NT
Thanks for such a quick reply. Sounds like the boiler stat is the problem. Any idea if there is an easy way to test the stat? Regards Dave
I think you just did! grin. Brian
"Dave" wrote in news:yPour.608047$ snipped-for-privacy@fx23.am:
There is a fair chance that the problem is not with the boiler but with the 2 or 3 port valve if the system is fully pumped.
What could be happening is the hot water valve is jammed in the open position and water being heated uncontrolably when the central heating is on.
To check, turn the boiler off for 2 or 3 hours then turn on heating only.
After a couple of minutes feel the pipe going to to the cylinder.
If this is getting hot then look for a faulty valve or actuator.
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Hi, thanks for replying. The problem with that is that there is no 2 or 3 port valve/s. There are only 2 x 1" copper tubes to and from the boiler to the cylinder. There are no external stats, the system is gravity fed and the only pump is on the feed from the boiler to the C/H. I've been looking for another stat for the boiler but as the boiler is around 40+ years old, parts are quite thin on the ground. Dave
If you have any kind of 'demand' signal that still works (timer, on/off) you could wire a new tank 'stat in series with that....
Better to change the boilers stat. You could end up with a cylinder of HW and no CH.
One thing is certain - the water in the cylinder *cannot* get any hotter than that being produced by the boiler. So if it's *too* hot, the water produced by the boiler is too hot. If this isn't reduced by turning the boiler stat down, the boiler stat is duff!
If you can't get a replacement boiler stat, you could fit a pipe stat to the flow pipe, and use that to interrupt the boiler demand.
Excellent idea. I've got the wiring diagram and it looks a simple matter of disconnecting the boiler stat at the control box, and wire in the new 'pipe' stat. Great, I'll start a.s.a.p. Many thanks to all. Dave
23.am4:
This cant be the cause. With boiler stat set low, the HW temp is exceeding the setpoint of the primary, which isnt possible. Primary circuit stat must be faulty.
NT
if it were mine I'd have a look at the existing stat contacts first, they may be wleded together. If so, part them and file the switch surfaces smooth with a rat's tail file. Now, doing this will have changed its setting a fair bit, so its important to watch closely during first run and slowly turn the stat down until it switches off once the primary circuit water gets hot.
NT
So it's done it's moneys worth. Time to start looking for a replacement I suspect that the efficiency of 40+ year old boiler won't be very good. You could make considerable savings in gas used... Take the opportunity to improve the control system as well for additional savings.
Probably not G rated so the boiler scrapage scheme might not help but a few minutes on the SEDBUK site might be worth while, though something that old might not be listed...
if it were mine I'd have a look at the existing stat contacts first, they may be wleded together. If so, part them and file the switch surfaces smooth with a rat's tail file. Now, doing this will have changed its setting a fair bit, so its important to watch closely during first run and slowly turn the stat down until it switches off once the primary circuit water gets hot.
I've noticed in the manual that it is possible to strip and maintain the thermostat valve. Seems straight forward enough, would it make any real difference?
Dave
I think the prize should go to NT ...... spot-on. I stripped the thermostat, cleaned the contacts and re-assembled it. The phial was cleaned with wirewool, smeared with heat tranfer silicon and placed back in the phial pocket. The boiler now fires up at different temperature settings as it should. I'm hoping that as I'm now able to control the temperature of both HW and CH it should also quiten the pump down a bit too (me thinking that the water in the pump was cavitating due the water being too hot !). Time will tell. Many thanks again to all those who helped on this thread. Dave
+1 on both points.
NT
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