Central Heating - Electrical/Control Problem

[pauldoc]

Hi,
Can anyone give me some pointers for this fault?

I have a traditional gas-fired CH/HW system with a gravity fed loft tank. Controlled by honeywell programmable thermostat and 7-day programmer.

A few months ago - sudden fault developed - the pump stayed on all the time even when the controller was off for both CH and HW. CH engineer checked everything (timer/thermostat/motorized valves etc) and said it was a short in the junction box - fixed problem perfectly. Strange as the junction box had not been opened since the house was built.

Now - the pump is going in the very early morning - about 5am - when the controller is off for HW and CH. It is causing the boiler to fire - the radiators stay off so it looks like the HW side.

I've checked and rechecked all the settings on both the thermostat and timer - all seem OK. I've had a look in the junction box and can't see any shorting.

The HW is definitely heating up at this time when the timer LED light is definitely off for HW & CH.

I suspect I'll need to call the engineer in again. But any ideas what this weird fault might be? Programmer fault? Faulty wiring somewhere? Could it be anything else?

Thanks for any ideas.

Paul

 

[bellairaphon]

Id have a look at the time that your hot water is set for.. if its a repetative pattern same time etc then i would go straight to timeclock. has it been reset? could just be that or could be on its way out.

 

[pauldoc]

Thanks - I'll definitely check this again, but I've checked the timings of this and they are OK. The clock time is OK. It works perfectly when we monitor it during the day and when we get up in the night/early morning to check the problem, the boiler is on, pump going... but the LED 'on' light for HW is definately 'off'. The LED fuinctions perfectly to indicate on/off when we can monitor it in the daytime. The timer is only a coupl of years old.

Paul

 

[seco services]

have you checked the mot valve if its a 2 port valve ?

 

[rebuke]

I had an identical fault with a Honeywell system in my house. It had a junction box that had labelled terminals for pump, motor etc etc, that was designed for a variety of systems. The lid of it had information on which wire links to cut for the different configurations.

It turned out, that while whoever installed it had cut the correct link for Y-plan usage, they hadn't read the bit at the beginning which said "If using a programmer rather than a simple timeswitch, cut link 1". This meant that the CH off wire was linked to the ON wire for the HW (or vice versa, can't remember), or something similar. This meant that if the cylinder stat called for heat, the boiler and pump fired up, even if the programmer thought everything was off - it was very confusing!

 

[seco services]

A few months ago - sudden fault developed

 

[rebuke]

I saw that, but I only noticed the problem with my system when I turned up the thermostat on the cylinder - so although it had been there all along, it did 'appear' to start suddenly, so I thought still worth mentioning as there's a chance that it could explain the problem...

 

[gas4you]

I would say it is a motorised valve head fault.

 

[D_Hailsham]

I have a traditional gas-fired CH/HW system with a gravity fed loft tank. Controlled by honeywell programmable thermostat and 7-day programmer.

Which boiler do you have?
Which programmable stat?
Does the 7-day programmer control both heating and hot water?
HOw many motorized valves?

checked everything and said it was a short in the junction box - fixed problem perfectly. Strange as the junction box had not been opened since the house was built.

Or was this just coincidence?