No Hot Water - Rads OK All aspects of plumbing questions and answers, help, tips and information

[DickEyeJoe]

Hi There,

I hope there is somebody here that can help me. My central heating works fine but my gravity fed hot water system has become rather cold in recent months. The plumber has serviced the Ideal Classic RS 250 boiler in addition to it's annual service last summer, replaced the radiator pump and added a chemical cleaner to the system. They have also extended the on time from a few hours in the morning and the evening to 20 hours and still the water is too cold for a comfortable wash or shower.

When the heating is off and the hot water is on I can often get the correct water temperature within 2 hours but this is not always so.

This system has worked very well for 8 years without any problems.

Any help would be very welcome.

[Dave From Leeds]

It would appear to me that you most likely have an airlock (or partial airlock) in the heating coil inside your hot water cylinder. If so, the air may have entered the system when the pump was changed. There are two ways that I can think of to try and clear it. The first one involves finding the supply and return lines between the cylinder coil and the boiler. These should enter the cylinder on the same side, one directly above the other.

Having located the pipes, slowly slacken but do not remove the union where the higher one of them enters the cylinder. The head of water in the CH top-up tank should then push any air in the coil out in the same way as bleeding a radiator. If some air does come out, keep the union undone until only water comes out then re-tighten it.

The other method is slightly more awkward. Fit a hosepipe over the open end of the vent pipe that goes over the top of your CH top-up tank. This is the smaller of your two cold water storage tanks, probably in the loft. Attach the other end of the hose to a (preferably mains fed) cold water tap. Get an assistant to slowly open the tap whilst you look into the top of the tank. If there is air in the system, you will see bubbles coming up through the bottom of the tank. Once the bubbles stop, turn off the cold tap then remove the hose.

If the nearest cold tap is not mains fed, the second method will only work if the water level in the larger cold water storage tank is higher than that in the CH top-up tank. It will also take longer to clear the airlock than if mains fed. The tap on your kitchen sink should be mains fed, whilst those in the bathroom may not be. Mine are.

Please note that I am not a plumber, just a keen DIYer. Good luck. Oh, and one last point, make sure that the hot water and CH systems are turned off when you do the work to avoid getting scalded.

[DickEyeJoe]

Thanks for your very detailed description Dave of the possible cause and cure. This follows my own thoughts that there could be an air lock, although not because of air ingress when the pump was changed. The pump failed two weeks ago and the rads went cold but the hot water was back to normal. After pump change the cold water problem returned straight away. I am not a confident plumber but will try your suggestions for the airlock and post back here. I also thought that if not an air lock, then maybe a blockage through sludge or even corrosion of some kind.

Once again thanks - DickEyeJoe

[DickEyeJoe]

I chose the second method because I couldn't find a suitable spanner and didn't want to use mole grips on the tank. I ran the mains cold water in to the vent pipe for about a minute. The water rose by about 20 mm but no bubbles appeared although I could see some minute particles.

After a full test it appears that the problem still persists and the hot water is still cool.

I am not sure for how long I should have run the cold tap or if the water actually went through the coil or found another route. Any further advice would be gratefully received.

Thanks

DickEyeJoe

[Dave From Leeds]

Only other thing I can think of, given you don't want to risk damaging the HW cylinder, is to shut off the supplies to your radiators and give it another go. Or maybe someone more professional than me could help.

[buildingserviceseng]

[quote="DickEyeJoe"]Hi There,

I hope there is somebody here that can help me. My central heating works fine but my gravity fed hot water system has become rather cold in recent months. The plumber has serviced the Ideal Classic RS 250 boiler in addition to it's annual service last summer, replaced the radiator pump and added a chemical cleaner to the system. They have also extended the on time from a few hours in the morning and the evening to 20 hours and still the water is too cold for a comfortable wash or shower.

When the heating is off and the hot water is on I can often get the correct water temperature within 2 hours but this is not always so.

This system has worked very well for 8 years without any problems.

Any help would be very welcome.[/Hi you dont say how your gravity system is temperature controled, in old systems there is a thermostatic valve on the return from the cylinder, this can be altered to change the temperature. It could be blocked or us. If you dont have this do you have a motorised valve ?]

[DickEyeJoe]

Thanks Dave, I will give it another go when I get some more time. I am beginning to think there may be some kind of blockage, perhaps sludge and the water found another route back to the header tank. The inlet (upper) union to the coil is extremely hot to the touch and the outlet is quite cool.

DickEyeJoe

[DickEyeJoe]

Hi buildingserviceseng,

I don't know how the hot water is temperature controlled. I have had a look behind the tank and around the boiler and can't see anything that obviously resembles a valve. I guess if there is one it may be under the floor in the bathroom or behind a tiled reveal in the kitchen. Originally, in the 80's there was a very old Potterton boiler with a clockwork timer mechanism feeding the gravity part of the system and any valve may date from then. Apart from pulling up floorboards and looking, is then any other method of locating a valve?

Thanks

DickEyeJoe

[DickEyeJoe]

The problem is now resolved, my plumber eventually drained and fully flushed and back flushed the system, it took about 5 hours start to finish.

The problem appeared to be due to sludge, lots of it, very thick and black.

I now have hot water and central heating together and in less than an hour from cold. I guess the system is so much more efficient without the sludge.

Thanks to the forum members that provided advice.

DickEyeJoe

[Dave From Leeds]

Pleased you've got it sorted. Thanks for letting us know. Most people never get back so we're left wondering if problems have been solved.