Halstead Best 80 Boiler Overheat Lockout

[spshannon]

The first few times we got an 'Overheat Lockout' it was traced to low water pressure and was easily rectified by topping up the water in the system.
Now we are experiencing 'Overheat Lockout' more frequently. It is easily cleared but I can't understand what is causing the problem - sometimes the boiler will work happily for 10 - 14 days before the Lockout recurs, but sometimes we are lucky to get a few hours of heating!
I'm not sure if we've got a sensor problem or something more serious. How do I go about diagnosing the problem?

 

[Gasguru]

Is the pump wired to the boiler - check the terminal strip in the boiler.

What controls/zone valves are there? With 2 port zone valves you should have a bypass valve after the pump.

 

[spshannon]

Yes, the pump is wired to the boiler.

I can't see enough (nor know enough) to be sure about zone valves.

I should say that this is a boiler installation in a new house built in 2001. The system has run without trouble for 6+ years.

Judging by some of the other comments I've seen, could we be suffering from sludge build-up? This is a very hard water area and the only other plumbing problems we have had is a blockage from washing machine caused by thick sludge.

 

[gas4you]

When it locks out is it on HW, CH or either?

 

[ChrisR]

Do you find it locks out after it has been on for long enough to get hot on its own internal thermostat -half an hour or so from cold?

 

[spshannon]

Not consistently, but this may fit a pattern.

I guess it depends much on the ambient temperature, but now I think about it there is often a lock out about half an hour after it has has been off for a period of time.

We usually have HW & CH on together but I think it locks out on either.

 

[hav it]

hi do you know what temp its locking out at.

 

[Andy165]

Had a halstead 60 best boiler locking out . Changed the ch pump, no joy. changed the overheat stat., no joy. Flushed the system, no joy. Turned the boiler stat. down from setting 6 to setting 4 which was still adequate, and working ok. Boiler had been relocated form one room to the next, and must have knocked the calibration out. Everything checked in the correct position and working ok

 

[Gasguru]

OP are you taking about the overheat LED (the one above the thermostat knob) or the ignition lockout neon (below the red reset button)?

 

[spshannon]

It is the Overheat LED - the one above the thermostat knob.

The thermostat knob position is set to 4. I have tried taking it lower and higher (but not to max. & min. settings) but this did not seem to make any difference.

There is one other indicator that behaves strangely. The water pressure dial can fluctuate from 0.5 to 3 bar over the course of the day. Is this normal because of expansion as the boiler heats up?