1. Home
  2. UK Do-It-Yourself Forum
  3. Ahhhhh!! HW still playing up

Ahhhhh!! HW still playing up

In a previous thread I described my problems with our lack of hot water. To recap CH system appears to be working fine but the HW supply is pitiful. We can only get a couple of inches for a bath before it runs cold. Only the top third of the HW cylinder appears to be warming up and even that takes forever.

The important info is

  1. Pumped CH, gravity fed HW system. Boiler has 2 large pipes running from the top up to the HW cylinder, and 2 pipes at bottom (one with the pump) for the rads

If it helps a pic of the boiler is here

formatting link
(no comments on the decor :)

  1. No 2 or 3 way or motorised valves
  2. No thermostat on HW cylinder
  3. Plenty of water in F&E tank and ballcock working OK. There is some slime around the edges though !
  4. I've bled the rads, but hardly any air came out before the water. Water wasn't particularly black.
  5. There's inhibitor in the system. Or at least it was replaced a year ago when the pump packed up and was changed.

Due to the slime mentioned in 4. I'm back to suspecting a blockage in the boiler > HW cylinder > boiler loop but is there any way of proving this.

Is it going to be worthwhile me taking the rads off and flushing them or will this be a waste of time if they appear to work OK.

Is it likely to be the valve thing in the pics. I was told this was a pressure release valve so don't think it has anything to do with the water temp.

Any help much appreciated as the Mrs keeps moaning !

Thanks Jim

ps. Can anyone give a quick explanation of how gravity system circulates. Can't get my head around what forces the water round the system with no pump.

Reply to
Jim
Loading thread data ...

heat/convection

Reply to
Gav

Not very easy. Try measuring the temperatures of the pipes to and from the cylinder. This can be done with a clip on pipe thermometer (about £10) or an infra-red one that you point at the object (about £20). Normally the flow temperature should be at about 82 degrees and the return at about 70.

If the flow temp is much less than this, then the boiler thermostat is set too low or is faulty.

If the difference between return and flow temperature is a lot larger than this and the boiler is cycling a lot, then it suggests poor circulation around the gravity circuit.

You would need to drain the system, disconnect some of the plumbing of the cylinder coil and flush the pipes between cylinder and boiler if it's this.

If the difference between flow and return is a lot less and the boiler is cycling a lot, then it is likely that the coil inside the cylinder is scaled up on the outside and not transferring heat to the water. If it's this, you could try to descale it by part draining the cylinder and putting in Fernox DS3 descaler.

The alternative would be to replace the cylinder. If you are going to do that, it would make sense to reorganise the plumbing and switch to fully pumped operation. Grateful females would be guaranteed.

I don't think so.

It looks like a pressure release valve, as you say. Normally these stick shut if anything but don't impede flow through.

Yes they do. You can certain address this issue. I can't help you with the perpetual moaning though.

Convection. Hot water is less dense than cold water and therefore rises towards the cylinder coil. Cold water falls from the cylinder coil to the boiler. This causes a natural circulation. It is wrongly described as "gravity".

Reply to
Andy Hall

Andy

Thanks for the comprehensive answer, no need for a thermometer I can tell just by touching the flow and return that there's more than a 12 degree difference between them !

Rather then spend too much time on what I suspect is a pretty knackered 30 year old cylinder I think I'll just swap it out.

I'll also take the opportunity of switching to a fully pumped system - so now a couple of questions about that.

Had a look at the Honeywell site and I guess I'll probably go for a Y plan setup so...

  1. Is it just a case of moving the HW flow from the boiler to after the pump. Would this cause any problems re expansion venting etc
  2. Do I cut off the old HW flow pipe and stop the end. ie so only 3 pipes used at the boiler
  3. I'd like to move the pump as well (just a bit lower so that it's behind some units) can they be mounted vertically
  4. Guess I'll also need a new programmer for independant HW and CH control. Is it simply a case swapping old for new and running additional wiring to the cylinder thermostat and 3 way valve?
  5. Any reason not to use push fit fittings ?

Thanks again for your help

Jim

Reply to
Jim

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.