DHW Cylinder Coil not heating water

clonshanny

Hi All,
I am wondering if anyone can help me with a problem i have. The water in the our DHW Cylinder is not heating. The flow pipe from the Stove has a T Junction. One pipe leads to the top of the cylinder and the other leads to the circulating pump which feeds the rads.
The pipe going to the circulating pump seems to be taking all the hot water and there isn't any hot water going through the coil.
Is it possible that this could be an airlock or could something have blocked the pipe from the headder tank in the attic?
Any help on how to solve the problem would be gratefully appreciated.

DoneDL

What is the stove stat set at and some pics would help.

clonshanny

DoneDL wrote: »

What is the stove stat set at and some pics would help.

The stat on the stove is just a dial with no's on it from 1 to 8, that i have set at 4. The heat from the stove isn't the problem as the rads have more than sufficient heat in them. The system we're using is a gravity fed open vented system, with the heat to the coil in the DHW cylinder supplied by convection from the stove. It was working fine up to yesterday when we noticed that the hot water wasn't rising in the flow pipe to the coil but there was plenty of heat in the water goint to the circulating pump and on to the rads.

Sorry, not sure how to upload pics. If i can figure it out I'll post some.

DoneDL

I would try turning up the stat to 6 and see if the cylinder heats. It could be that the stat is misreading.

clonshanny

Some pics of the system we're on. The problem area seems to be on the rising pipe to the top of the coil.

clonshanny

DoneDL wrote: »

I would try turning up the stat to 6 and see if the cylinder heats. It could be that the stat is misreading.

Tried turning up the stat on the stove to the max but the water in the boiler was starting to bubble so it was obviously getting too hot.

DoneDL

Dont turn the stat to max. If the pipe is heating and turning on the pump at the correct temperature then the coil may be airlocked. Do not try to clear any airlocks when the stove is on.
I would also check that there is water in the F&E tank.

clonshanny

DoneDL wrote: »

Dont turn the stat to max. If the pipe is heating and turning on the pump at the correct temperature then the coil may be airlocked. Do not try to clear any airlocks when the stove is on.
I would also check that there is water in the F&E tank.

The feeder tank is full with water so that doesn't seem to be the problem. I wont drain the system or try anything while the stove is heating the water. I might drain the system tomorrow, disconnet and remove the pipe where the hot water isn't flowing and see if its blocked. At least if its airlocked, draining the system should solve it.

Thanks for advice DnoneDL. Will let you know how it goes.

Billy Bunting

Agree With DoneDL, Check expansion tank.

Billy Bunting

Carefully crack open the tee the vent comes out of and make sure there is water there.

clonshanny

Billy Bunting wrote: »

Carefully crack open the tee the vent comes out of and make sure there is water there.

Tried that one too and there was plenty of eater there.
At least the cause is being narrowed down a bit.

TPM

Was the DWH cylinder working before now?
Was there any work done in the hotpress?
Make sure the valve !!! on the feed pipe is turned on, the black handled valve.

Check the pipe stat, is it turning on and off? if it has the circulating pump running all the time the cylinder will struggle to heat

clonshanny

TPM wrote: »

Was the DWH cylinder working before now?
Was there any work done in the hotpress?
Make sure the valve !!! on the feed pipe is turned on, the black handled valve.

Check the pipe stat, is it turning on and off? if it has the circulating pump running all the time the cylinder will struggle to heat

Yes the DHW cylinder was working fine all along and there wasn't any work done in the hotpress. The valve on the feed pipe is fully opened and the stat for the pump is turning on and off ok.
Our water is very hard though and the immersion heater has to be changed every few years after the limescale has eated through the one in the cylinder. The coil maybe covered in limescale too but its hard to imagine how that would occur when the coil would never get as hot as the electric heater.

I'll try draining the system and seeing what happens when i refill it.

shane0007

It's an odd one alright. I would have thought lime scale would have been a gradual issue and not sudden. It sounds more like a blockage. Perhaps something got into the system through the f & e tank and got stuck in the coil.

Let us know how you get on as I have a similar problem to deal with next week. Booked to replace oil boiler next Wednesday and they then rang me to say solid fuel has suddenly stopped heating the water but heats the rads ok.

clonshanny

shane0007 wrote: »

It's an odd one alright. I would have thought lime scale would have been a gradual issue and not sudden. It sounds more like a blockage. Perhaps something got into the system through the f & e tank and got stuck in the coil.

Let us know how you get on as I have a similar problem to deal with next week. Booked to replace oil boiler next Wednesday and they then rang me to say solid fuel has suddenly stopped heating the water but heats the rads ok.

I will drain the system and remove the section of pipe where the blockage seems to be. Ive got a pipe unblocker (those aldi ones for kitchen sinks etc) so i'll put that through the coil and see if there's any kind of a blockage there.

Yes i'll let you know how it goes.

jimjimt

Anything is possible. I have found a few bats stuck in fittings and tees from time to time.

If your coil was overburden with lime it would be a slow progression. Each year it would take the cylinder a little longer to heat up. Which would eventually stop the coil from heating the cylinder but the flow pipe should still get hot.

How long is your cylinder installed ?

clonshanny

Finally think i have the problem solved although no idea what was causing it. I drained the system and removed the section of pipe where the heat seemed to be stopping. I put the drain unblocker through the coil and there didn't seem to be anything in there. After putting pipes back together i refilled the system and started the fire. When the heat built up, the water started to circulate through the coil and back to the boiler through the return. Everything seems to be working fine now so anyone's guess is as good as mine as to what the problem was.