No Hot water but water coming from hot taps?

pontiac22

First time posting so bear with me.

Had an air lock in the system on Sunday. Eventually got a plumber to unlock it as my own efforts just didn't crack it.

Although there is water coming from the hot taps its cold. The pipes from the immersion are hot, the rads are hot, but there is no hot water coming from the hot taps. I thought maybe as the tank had run empty, with it having to be refilled it would take time for the immersion to heat & retain the hot water. As it previously has always done. Now, if i put on the immersion heater I get hot water but it goes cold after a short time. I've never had to use the immersion heater, I assumed with the gas boiler the tank heated the water & the rads therefore we always had hot water.
The plumber told me it was a top filling tank from the attic. All he did was open the feeder pipe to the tank, released the air & reconnected the filler from the attic. I watched him throughout. He didn't touch any other pipes or turn anything off.
Would it be the thermostat inside the tank? Could it be an element issue?
The immersion is per-insulated. I would have though with the gas boiler on heating the rads that it would also heat up the tank?
Another thing I noticed was that the pressure gauge on the boiler is above 2.5 psi (I think that's right?) almost at 3 when its on. Should I be concerned about this? How do I get the pressure down? And what will the impact of a high pressure be?
Would really appreciate any assistance.
Thanks.

nmacc

Not quite sure that I follow the explanation, but it sounds like your plumber cleared an airlock in your hot water system, but now the water from the hot taps runs cold?

This should have nothing to do with the central heating and if the pressure is at 2.5 Bar when cold, then it is too high. This could be completely unconnected to the lack of hot water.

Your hot water cylinder (not 'immersion', the immersion is the electric heating element in the cylinder) heats from the gas boiler because there is a coil of pipe inside it acting just like a submerged radiator. Assuming that you don't have a Hot Water channel on your timeclock that is set to Off, then water should flow through the coil when the boiler is on, but a couple of things can stop this.

If there is air in the central heating it can sometimes collect in the coil in the cylinder as it may be the highest point in the system. If this happens then the pipe from the central heating system will be cold where it enters the hot water cylinder and you'll need a plumber to clear the airlock, unless you're feeling competent to take it on.

However you mentioned the pipes were hot, in which case I'd suspect the balancing valve. It looks like this and it should be in the return pipe from the bottom of the heating coil. It controls how much of the central heating water flows through the coil. Too much and the radiators won't heat properly, too little and the cylinder won't heat.

It should usually be open only a small amount. When there's a problem with the water system folks often open & close all the valves in the hot press to try and fix it. Check this valve hasn't been left closed.

As far as the system pressure goes, then it may need to be reduced. There could be a filling valve in the hot press that was opened and raised the pressure. Check for water from the boiler safety valve when the system is hot and the pressure high. If it's not dripping water then I'd be tempted to leave it for a week or so and see if it drops by itself.

pontiac22

Thanks nmacc

Appreciate all the work in your response. Thank you.

I'd be fairly OK in the DIY. Would feel competent enough to tackle most jobs. Just like to have all the information to hand to ensure I'm doing it right.

Assuming there is an air lock in the coil, how do I go about clearing it?
Although, as I said earlier, the pipes are hot coming from the tank to the rad pipes next to the tank.
So your other assumption would seem to be the more logical answer, that being the Balancing Valve.
Should I then close it to its fullest & progressively open to a certain point? In the hope that this will even out the flow?

nmacc

I'd suggest starting by opening the balancing valve fully. That way you should get full flow through the cylinder coil at the expense of the radiators. If that works then you have found your problem. You can then close it down too bring up the radiators. Usually the balancing valve is only open a small amount, say 1/2 up to 2 turns, but it depends on the installation.

If there is air trapped in the coil piping then opening the balancing valve is unlikely to help. You need to go to the top of the cylinder coil where the water from the heating system enters the cylinder. There's usually an elbow at this point and there might be an automatic air vent like this:

If so, then open the cap and the trapped air should be released - don't drop the cap; after a few years these vents usually leak so you may need to put it back quickly. The cap may look like a tyre valve cap, but they rarely fit.

If there's no vent then you'll need to carefully open the joint a few turns, assuming it is a compression fitting. Do this with the heating off and a towel around the pipe. Be careful not to undo it completely as you may have to pull the pipes apart slightly to let the air out.

If the system is on then the pipes may get very hot as the air is replaced by water, so be ready for this. Conversely, if the joint is already hot then there is no trapped air and the problem lies elsewhere.