No hot water

short_frank

Hi,
My heating (underfloor heating) has been off all summer and the oil has only been heating the hot water. This ran out a couple of weeks ago but we didn't bother getting any more till today as the weather was good and we just used the immersion. When we refilled it started fine but the hot water tank never heated. Now we are getting no heat because the return is hot and so the system is not calling for heat. I know it is probably an air lock but how do I clear it.
I have connected the hot to the cold tap and tried to flush the air out but no good. I have a small red round tank (overflow I think) under the main tank and this is full of hot water.
Any help would be appreciated.

JamesM

If the boiler has started up OK, it is likely that your water pump is stuck because it was off for a while - it may not be an airlock. If there is water coming from the tap, connecting the taps will do any good. Try tapping the body of the water pump gently with a hammer or something similar to free it. The red tank is probably an expansion vessel, so you have a sealed system. It may need to be topped up.
Jim.

tapest

short_frank wrote:

Hi,
My heating (underfloor heating) has been off all summer and the oil has only been heating the hot water. This ran out a couple of weeks ago but we didn't bother getting any more till today as the weather was good and we just used the immersion. When we refilled it started fine but the hot water tank never heated. Now we are getting no heat because the return is hot and so the system is not calling for heat. I know it is probably an air lock but how do I clear it.
I have connected the hot to the cold tap and tried to flush the air out but no good. I have a small red round tank (overflow I think) under the main tank and this is full of hot water.
Any help would be appreciated.

Hi Frank
As James m says , the red small tank is an espansion vessel, and is there to "absorb" the pressure difference in system when hot.
Blowing air lock back to header tank by connecting MAINS cold tap to DRY/"EMPTY" hot tap usually works for air locks in the DOMESTIC hot water system...BUT you problem is not in the domestic system. Your problem is in the central heating water circuit...both are completely separate..ie the water from these different circuite never mix, even in the copper cylinder.
The reason "the return is hot" on heating circuit is ..once you generate heat at boiler it will rise through pipework (feed and return) by itseff ( hot air / water always tends to rise), but not very efficeintly sometimes depending on pipework layout. Because the generated heat can't "get away" the boiler shuts down on temp control. If all pipework and copper tank etc were directly above boiler, with very little sideway pipe runs it would be more efficient and the "return pipe" would not get as hot as fast...better heat dissipation.

END OF LECTURE
Back to your problem...
From your post..."system off for a while" ( usually longer than 2 weeks ?) I'd bet my bottom dollar the problem lies in the circullating pump. Probably just stuck.
But, with all due respect to Jamesm, I woudn't go smacking it with a hammer. Locate the pump bleed nut (very large slotted nut in the dead centre of pump motor housing). Unscrew it with a large coin (you might require a vice grips on coin) (this is how you bleed air from pump) and water should start dripping out. Do all this with heating boiler off. with large pot underneath, remove screw fully. Inside you will see pump main shaft, again with screwdriver slot, Turn boiler on and see if motor is turning. If not turn heating offagain and using large screwdriver "rock" the shaft back and forth to free shaft / pump.

Apology for long windedness
t

JamesM

I did say:
"Try tapping the body of the water pump gently with a hammer or something similar to free it." I did not recoment "Smacking" it :eek:

I would still try this before opening the nut, which can sometimes leak after you tighten it up again.
Jim.

short_frank

Thanks for the ideas, I have the heat to the underfloor flowing fine but still no hot water to the tank. I have perfect flow of cold water from both hot and cold taps. I have bled the system from the pump and the bleed points but still no difference.
I am getting a tad annoyed with it now so any help to stop me attacking it with a sledge hammer would be great.:D

JamesM

short_frank wrote:

Thanks for the ideas, I have the heat to the underfloor flowing fine but still no hot water to the tank. I have perfect flow of cold water from both hot and cold taps. I have bled the system from the pump and the bleed points but still no difference.
I am getting a tad annoyed with it now so any help to stop me attacking it with a sledge hammer would be great.:D

It could be that there is a lack of water in the system, especially if the cylinder is at the highest point. Or, if you have a thermostat controlling a motorised valve for the hot water side of things, the thermostat could have been turned down, or the valve has stuck because it was off for a few weeks.
Jim.

tapest

JamesM wrote:

I did say:
"Try tapping the body of the water pump gently with a hammer or something similar to free it." I did not recoment "Smacking" it :eek:

I would still try this before opening the nut, which can sometimes leak after you tighten it up again.
Jim.

HI JamesM
If I stepped on toes...apologies offered and I hope accepted.
The few times I tried a tapping (always using wood...big screwdriver handle or mallet) I had no results. I would be nervous recommending a light tap with hammer as my light tap mighy equate to a heavy hit by someone else. And those motor casings are cast and therefore brittle.
Anyway as mentioned above ...was not intention to cause offence
regards
t

stapeler

Can you feel any heat on either pipe going into the side of the copper cylinder from the boiler?? One suggestion would be to loosen the primary circuit line on the cylinder and check for air lock. It's the upper copper line on the side of the cylinder. Loosen it slightly with a towel underneath.

JamesM

tapest wrote:

HI JamesM
If I stepped on toes...apologies offered and I hope accepted.
The few times I tried a tapping (always using wood...big screwdriver handle or mallet) I had no results. I would be nervous recommending a light tap with hammer as my light tap mighy equate to a heavy hit by someone else. And those motor casings are cast and therefore brittle.
Anyway as mentioned above ...was not intention to cause offence
regards
t

Sorry if my reply was a bit sharp - certainly no offence meant or taken
But I have found on many occasions, 3 already since the season started in Sept, that a sharp tap with a vicegrips has worked. As you say, its down to experience and knowing how hard to tap
Anyway, he has now said that his underfloor is working, so the problem is not the pump.
Jim.