Calling any Domestic Heating Engineers on the forum

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Charles
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Calling any Domestic Heating Engineers on the forum

Post by Charles » Fri Dec 06, 2013 8:45 pm

If there are any members here with experience of domestic central heating & unpressurised hot water systems, would they mind making themselves known to me - by PM if you prefer - as I have an annoying problem that I need to try and diagnose/fix.

Many thanks

Charles
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Post by ali » Fri Dec 06, 2013 11:17 pm

Hi Charles
I'm a property maintenance contractor and have a bit of central heating experience as well as electrical and plumbing to name a few of my skills.
Whats the problem you have ?
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Post by BMW540 » Sat Dec 07, 2013 12:36 am

I am a real estate manager, so I know a lot about central heating systems.
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Post by Charles » Sat Dec 07, 2013 12:10 pm

Thanks chaps :D

Scenario:
Radiators and unpressurised hot water tank fed on two systems by a single boiler and controlled by a multi-controller. Controller showing "on" signal to both systems. Radiators hot but no hot water.

Diagnosis (so far):
Boiler working
Pump working
Radiator zone valve working
Radiator thermostat working
Hot water zone valve closed
No work has been done on the system and it is unlikely that any of the components have been damaged due to their location, leading to a failure as described

Intervention:
Manually opened hot water zone valve - opened easily without being forced but returns to closed position unless locked into open position - hot water starts flowing to tank coil - valve not "stuck" - water heats up as normal

Conclusion (so far):
Hot water zone valve not opening due to a number of possibilities
- signal from controller not received
- tank thermostat faulty
- motor for valve not operating

That's where I've got so far. I'd like to try and find the culprit before either fixing it myself or getting someone in to deal with the problem quickly, rather than them poking about and sucking air through their teeth before quoting me a stupid figure for a simple fix!

Any thoughts and suggestions?
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Post by BMW540 » Sat Dec 07, 2013 12:49 pm

Every (new) system has a pump to feed the radiators with hot water but some systems also has a pump that feeds the "radiator" in the hot water tank. The pump that feeds the "radiator" in the hot water tank is usually small and hidden. Does your system has such a small pump ?
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Post by Charles » Sat Dec 07, 2013 2:16 pm

BMW540 wrote:Every (new) system has a pump to feed the radiators with hot water but some systems also has a pump that feeds the "radiator" in the hot water tank. The pump that feeds the "radiator" in the hot water tank is usually small and hidden. Does your system has such a small pump ?
Not that I am aware of - just a single pump driving both systems as required.
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Post by BMW540 » Sat Dec 07, 2013 3:07 pm

If there is a little pump it should be close to the hot water tank and ofcourse it needs electricity, so you can find it by following the wiring, if there is any wiring near the hot water tank.
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Post by PerryGunn » Sat Dec 07, 2013 4:38 pm

Do you have a multimeter (and know how to use it)?

Assuming standard wiring, check the voltage across the brown and blue valve wires with the hot water on at the controller and the tank thermostat turned up so it's calling for heat, it should be 240V. If it is, the valve motor is faulty - most decent valves allow the motor assembly to be replaced without draining down

If not, it's likely either the thermostat or controller is faulty, or it's possibly a wiring fault.

Work your way back up the chain with the multimeter - thermostat output, thermostat input, controller output until you find 240V then you'll know the faulty component is the previous item (or the wiring between the two)

NB if you're not completely comfortable/competent dealing with electrics, don't touch it - get someone in
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Post by Charles » Sat Dec 07, 2013 8:27 pm

BMW540 - Definitely no little pump!

Perry - Just dug out the multimeter - if you don't hear from me again on here then you know it's gone horribly wrong!!!

Thanks once again to you all
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Post by Chas » Sat Dec 07, 2013 9:26 pm

I'd go with the controller being faulty. Many of them have a reset function which is like switching off a Windoze PC; worth a shot. Failing that it's the zone controller which is a bit more complicated but still diyable.

In the meantime, do you have an electric immersion heater in your water tank as a back-up?

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Post by Peter&Janet » Sat Dec 07, 2013 9:35 pm

Hi Charles couple of thoughts:

You may read the voltage on the pump motor but the wiring inside can also be open circuited & the impeller may have fallen off.

Thermostat not working, test by simply bridging it out with a loop wire as it's a switch. Assuming it's an old system but if it's digital and uses a resistance wire, can short the PCB.

Zone valve opens too freely, spindle possibly sheared

Is the header tank full and the radiators/pump all bled.
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Post by Charles » Sat Dec 07, 2013 10:38 pm

Loads of suggestions - thank you.

The system pump is functioning fine, as the radiators are being supplied (all of which are fully bled). The header tank is full, also. As such, the problem centres on the electrical parts of the hot water zone - controller, stat and zone valve - as the zone valve will open and close manually.

There is an immersion heater but my current work-round is to open the hot water zone valve manually and lock it open. This means that when the radiator system is open, the hot water system is open too, thereby heating both radiators and hot water tank. The boiler heats up to 65oC which is what the hot water stat is set to so, once the hot water tank has reached that temperature, it won't get any hotter as there won't be any further heat transfer to the hot water in the tank. This then means that all the heat generated by the boiler is sent to the radiators which are controlled by the stat.

My only thought about this is that, by keeping the hot water system "open", the stat (if working) won't close the valve and so the boiler may continue to run. However, if there is no heat removed then the boiler will shut down as the system water will stay at the maximum temperature.

Not ideal but at least we have hot water.
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Post by JASV8S » Sun Dec 08, 2013 4:10 pm

Charles, your system set up is like mine and I have had this same fault twice and both times it was the zone valve. My system has Honeywell valves and you can change the motorised actuator without removing the valve head avoiding draining down. The failures were about 12 - 15 years apart so reasonable life span. I also took the opportunity to change the other zone valve as it was 20+ years old when the one failed last year.

If you have good access to both valves you could swap over the actuators and see if the fault swaps over.

Because of the time that passed since the previous failure and I decided to replace both valves I took the opportunity to drain system down, give it a flush. Just as well as one of the valve bodies was quite chocked up with gunge which must have been restricting the flow.

Sods law as mine packed up at this same time of year last year and it was Baltic up here in Aberdeen.
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Post by Bruce M » Tue Dec 24, 2013 12:32 am

Did u get this sorted Charles?

If you are careful (very!) you can figure it out with a volt meter and a length of wire. All the wiring will end up at a junction box. From there you can check where the 'signal' from the timer is stopping. As said this is 240v so be careful.

I had a similar problem and linked the hot water circuit to the radiator circuit as a test. That fixed it so I knew the valve was working. When I removed the timer (guessed it was broken) I found a wire had snapped (the installer had been over enthusiastic with the wire strippers).
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Post by Charles » Tue Dec 24, 2013 7:14 pm

I have a spare zone valve actuator and this is on the list of jobs between Christmas and New Year - so I'll report back in due course.
Charles
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