Not very hot DHW - Any ideas?

[GMM]

My hot water tank has stopped getting properly hot. The heating is working fine, so it's unlikely to be a boiler issue. The pump seems OK and the thermostat ~seems~ to be operating fine (on the basis of a click as you turn the knob). There's no air in the circuit judging by the bleed valve. I'm tempted to replace the thermostat, just cos I can, but I'm not convinced that's going to achieve anything.

Any (sensible) suggestions would be appreciated.

Standard open vented indirect tank and boiler with nothing fancy like weather compensation etc. No recent issues. DHW timer set to run when the heating is off.

Cheers people

[Peter Able]

Can you feel hot water entering the DHW coil as and when it should?

PA

[Tricky Dicky]

Faulty valve or diverter

Richard

[Chris Hogg]

What sort of DHW/CH system is it? S-plan:

? or Y-plan: ?

If the first, the zone valve in the DHW circuit on the LHS in the diagram may have failed, or the controller isn't sending the 'open valve' signal correctly.

If the second, the mid-position valve may not be working properly and be stuck in the CH position.

[Harry Bloomfield, Esq.]

GMM used his keyboard to write :

Has the boiler flow temperature been reduced?

Check the cylinder stat temperature setting?

Check the HW time clock is on for long enough?

Check an HW tap has not been left on.

[Harry Bloomfield, Esq.]

Harry Bloomfield, Esq. explained :

Check the 3-port valve is properly switching to heat the cylinder.

[GMM]

I've puzzled over those sort of diagrams in the past and neither fits the situation precisely, but I suppose the S-plan is the closer (mine splits to two separate pumps, with a valve on the heating circuit after its pump. No valve on the DHW side apart from the thermostat-controlled bypass) So far as I can tell, both valves are operating correctly, as are both pumps, which is why I'm a bit lost in terms of th mechanical side of it....

[GMM]

It feels hot but of course I haven't held onto the pipe for the full time the boiler is running....

[GMM]

They seem to b operating OK in terms of opening/closing when given a signal...

[Chris Hogg]

There are the ?older C-plan

W-plan both diagrams taken from but if you have two pumps that doesn't seem to fit either type.

Do you know that the pump is actually working, as opposed to just making a buzzing noise or vibrating? Are you in a hard water area? If so, is the coil in the DHW tank furred up? Is the tank thermostat shutting off too soon? What happens if you turn it up to somewhere near full on?

[Andrew]

When the DHW circuit is pumping, how hot are 22mm pipes feeding the tank ?. Do you have a clip-on thermometer or one of those laser ones to see what temp of water is arriving and leaving the tank.

[Andrew]

If your boiler is supplyng water at 80+ C then it wouldn't 'feel' hot, it would be 'ouch, fkit' hot. Can you check your 3way valve and make sure it is operating properly ?.

[Glenn Matthews]

Yup - that's about the temperature (!) I'll see if I can get my IR thermometer on it later and find out roughly what 'ouch fkit hot' equates to....

[Peter Able]

Can you explain this? A bypass of what?

PA

[Vir Campestris]

IR thermometers aren't very accurate on shiny pipes. You might want to stick some opaque tape on it.

See

AKA

Andy

[Tricky Dicky]

Yes! The cylinder should be controlling a valve. Bypass? that I am familiar with have no electrical connection being simple mechanical devices that you set separate on the bypass.

[Peter Able]

Had to read that a couple of times. The plural of Bypass is Bypasses. As you describe, relatively dumb, set and forget components - which could be in parallel with the DHW coil. If so, and set fully open, problem identified - maybe!

Any response, GMM ?

PA