No Hot Water

[ub7rm]

Hello,

System is a pressurised hot water cylinder (Megaflow) fed from an oil fired boiler. There are two motorised valves in the garage, one for the CH and one for the hot water.

When I put the hot water on on the timer it clicks and the light comes on but neither the pump or the valve actuates and the water in the tank is stoney cold. CH works fine.

I tried forcing the HW motorised valve open and that doesn't prompt any thing to fire into life.

I've left it manually open with the heating on to see if that gets some temperature into the cylinder. The immersion heater doesn't seem to work. Not surprising I suppose as its not been used for the last 10 years.

I'll be getting a plumber out on Monday, but whats the likely cause? Programmer not working or thermostat in the tank not calling for heat?

 

[Doggit]

Put the central heating on, and then open the valve. You may be able to then close of the CH valve, but it's working on a different set of rules. Do you know if the cylinder stat is working.

 

[ub7rm]

Hadn't thought of shutting the CH valve. Would that not shut the boiler down? Seems to be heating the water up now, though I've had to turn the room stat up to keep the boiler firing.

I'm not sure if it is or not to be honest. How would I check?

 

[Doggit]

You'd need to test the output from the thermostat to see if any voltage is passed through when the temperature is changed. There are other her that can lead you through that better than I can.

The room stat is calling for heat from the boiler, and as the heat is going into the tank rather than the radiators, then the boiler should carry on working, and it shouldn't have been necessary to turn the stat right up.

 

[ub7rm]

Thanks, it probably wasn't necessary but the house was already quite warm so the heating shouldn't have needed to come on in normal circumstances if that makes sense.

 

[steve32]

Have you checked the overheat stat on the megaflow hasn't tripped.

 

[ub7rm]

How far does it poke out when its tripped? It is protruding about a mm or so - would expect it to be further out if it had tripped?

 

[ub7rm]

Another question - this has an immersion heater in it - is the tank stat interlinked with the immersion heater stat or is there two separate stats? Because despite what I said above the immersion heater does appear to work - its just very slow. So if it uses the same stat as the indirect heating system then it suggests that the tank side controls are working and the fault is either with the programmer or the 2 port valve.

If they use separate stats then I guess that means nothing.

 

[Echo the husky]

There are 2 separate stats. Check for 240V at the brown and blue wires on the hot water valve when hot water is switched on. If it is there then the valve actuator is faulty, and needs replacement. If there is no 240V then there is either a programmer or thermostat problem. If all the water in the cylinder is heated already with the immersion heater, the thermostat that controls the valve may have clicked off already, and won't supply power to the valve, so watch for that if you find you have no power.

 

[ub7rm]

OK - might have a look at that later. Lastly is there a safety concern with what I've done (bypassing the tank control valve to get the heating circuit to heat the water)? I guess its now being regulated by the CH water temperature of around 80 deg rather than 60 deg by the tank. But other than the hot water potentially getting hotter than normal is there a concern? Won't be like this forever - just till someone fixes it next week.

 

[dilalio]

Just leave the valve manually open for about 45mins, then close it. The water in the cylinder should stay hot for about 24hrs or until you use it up - then you'll have to manually open it for another 45mins again. Or just rely on the immersion if it's working. It'll get you by in the short term!

 

[ub7rm]

What is the logic of the heating system?

Programmer on = 240V to the tank stat.
If the tank stat is calling for heat it closes and 240V goes to the 2 port valve?
When this actuates to open a microswitch closes and power goes to the boiler and the pump?

If the above is true, then when I manually open the valve it should hit the microswitch and thus switch on the boiler and pump?

I ask because I opened the wiring centre and found 240V at the gray cables going to the valve, and then when I switch the HW on at the programmer I got 240V at some orange wire going to the 2 port valve. So 240V appears to be going to the valve, so why doesn't the boiler kick in when I manually actuate the valve open?

 

[dilalio]

What is the logic of the heating system?

Programmer on = 240V to the tank stat.
If the tank stat is calling for heat it closes and 240V goes to the 2 port valve?
When this actuates to open a microswitch closes and power goes to the boiler and the pump?

If the above is true, then when I manually open the valve it should hit the microswitch and thus switch on the boiler and pump?

I ask because I opened the wiring centre and found 240V at the gray cables going to the valve, and then when I switch the HW on at the programmer I got 240V at some orange wire going to the 2 port valve. So 240V appears to be going to the valve, so why doesn't the boiler kick in when I manually actuate the valve open?

Because the travel on the motorised valve, when manually opened, doesn't depress the microswitch - it's a safety feature.

 

[ub7rm]

Many thanks again, having studied the wiring diagram, traced the wires and measure the change in voltage when I switch the HW on or off I'm sure its the 2 port valve that's goosed rather than anything in the tank and so I'm going to replace the syncron motor myself.

 

[ub7rm]

Just to close this out, bought a replacement syncron motor from Screwfix, chucked it in and all is now working as it should.