No hot water. 3 ladies in the house. I'm feeling the heat (but not from the water)

[Mike Jones Amber Hill]

Here's the problem:

• Central heating (wet underfloor) is fine.
• Hot water comes out of any tap/shower for 60 seconds, then cold.
• This happened suddenly, was working fine before that.
• Boiler working OK.
• Pipes within a couple of metres of unvented cylinder are hot.
• Pressure gauge to cylinder is broken (so can't read input pressure)
• Supplied by water main, good pressure in house generally.

My Theory:

• Water is hot in the cylinder and therefore heats up water in the pipes gradually.
• Whet tap turned, hot water in pipe comes through. This quickly runs off and only cold water follows.
• So, the hot water in the tank is not being pushed through the pipes, it just stays in the tank.

Is that a good theory? And if so, what would cause this? Tried turning of mains input to cylinder, opened hot tsp til it stopped, twisted the tun dish for a bit, refilled and the closed the hot tap. Didn't fix it. I am thinking do I need to drain the cylinder completely via the drain valve at the bottom, then refill? Also, could it be the silver automatic valve causing the problem? I actually have two cylinders side by side so hard to see how both ports would fail at the same time?

Any help? The ladies will be home soon 🙁

 

[Gasmk1]

you have 2 cylinders i cant see both 2 port valves failing so possibly not calling for heat check your clock. if calling for hot water check the small lever on the 2 posts on the cylinder the valve with the silver box it has a lever on the side if open (lever loose) then its open if its stiff and yoiu need to push it then its broke but you have immersion heaters on each cylinder two electric switches under the big red vessel. these should see you ok till you can get someone in

 

[bacon_sandwich]

I see you have a secondary pump yellow bronze thing in pic. I assume this is a large house. So check controls are set to hot water on, check both zone vales feeding the tanks are open (little lever at the side indicates this), put your hand on the bronze pump to see if it is warm, run the hot tap and check with your hand the water is leaving the cylinder, leave the hot tap on a long time to see if eventually it comes through at the tap. If you have good pressure at the hot tap, its going to be an issue with controls, valves and secondary pump, assuming boiler is functioning normally for CH.
cheers

 

[dancinplumba]

please don't mess, unvented cylinders can be dangerous, you need a G3 registered plumber

 

[Chalked]

If it’s been fine until now, it’s probably a shower mixer cold crossing into ththe hot.
Looking at the install there’s no balanced cold connection.

 

[Mike Jones Amber Hill]

Honeywell boxes both loose lever and resting on the auto side. Tim

 

[Mike Jones Amber Hill]

When the timer is off, honey wells are resting loose lever at auto side and the elbow from cylinder to box is only warm. Switch on timer, and elbow warms up. Lever stays resting in auto but seems to have a little more resistance (only slight)

 

[Mike Jones Amber Hill]

The yellow pump was apparently put in to help hot water get to the loft room. The guy who owned the house said he only turned this on in the winter. In fact we've never needed to use it. The timer for is powered, but set to off and always has been so don't think this is a factor.

Ran kitchen hot tap, warm then in 10 seconds cool. Tested for 2 mins, stayed cool. Water in both cylinders at 65 degrees and hot to touch (tested by opening into tundish and feeling - now have sore finger!)

 

[ShaunCorbs]

run the kitchen tap for a good 10 mins hot only does it get warm ?

 

[Chalked]

Could be drawing back up the secondary return .
Try turning both of the blue valves connected to the pump/cylinder.

Those should have non return valves fitted to stop that.

 

[Gasmk1]

View attachment 35583 When the timer is off, honey wells are resting loose lever at auto side and the elbow from cylinder to box is only warm. Switch on timer, and elbow warms up. Lever stays resting in auto but seems to have a little more resistance (only slight)

They are not opening you should be able to push them over ( they should be in open position)

 

[Mike Jones Amber Hill]

Running hot tap. Started very not for 5 seconds, then cool for 30 seconds, now cold after 1 minute and still cold after 10 minutes.

Re the blue valves, which ones (see pic) and what do these normally do, is it ok to leave them turned off?

One more clue, when I turn off the cold water main where it enters the house, the hot tap in the kitchen drops pressure by about 60%, turn the main back on and starts running but is colder.

So I think the basic question is what can stop the hot water getting from the tank to the taps?

 

[Mike Jones Amber Hill]

I assume there's no connection with what goes on around the manifold?

 

[ShaunCorbs]

Turn 1 and 3 off for ch suggestion

Can you turn the red ones off as well at the top of the cylinders then open a hot tap does it stop ?

 

[Mike Jones Amber Hill]

Ok, will do in a minute.

On the two port Honeywell valves, both levers are loose when timer calls for heat. When timer in off position, lever doesn't move, but can be manually pushed from auto to open, but you can feel the mechanical resistance when doing so, so I think these are working fine.

 

[ShaunCorbs]

Yep working fine

 

[Mike Jones Amber Hill]

Ok, 1 and 3 are in closed position, as are the red valves at the top of each cylinder. Hot tap in kitchen run for 1 min, and it is running just as strong as before and at the same temperature I.e near cold.

 

[ShaunCorbs]

Sounds like you have something back feeding then if it's still running could be a shower or mixer tap nrv failed

 

[Mike Jones Amber Hill]

We do have a bath thermostatic mixer that seems to be faulty, could be the problem? I'll need to get someone in, could you explain how you'd go about testing to find the problem - we've got 7 mixer taps and 4 showers in the house!

 

[ShaunCorbs]

We do have a bath thermostatic mixer that seems to be faulty, could be the problem? I'll need to get someone in, could you explain how you'd go about testing to find the problem - we've got 7 mixer taps and 4 showers in the house!

Yes can you isolate that ?

That's the fun part

In short isolation each until you find the problem one

 

[Mike Jones Amber Hill]

If the mixer (tap or shower) is off, how can they back feed? Are the hot and cold connected before they meet the mixer valve I.e mixer valve closed - doesn't that close both flows!

 

[ShaunCorbs]

If the mixer (tap or shower) is off, how can they back feed? Are the hot and cold connected before they meet the mixer valve I.e mixer valve closed - doesn't that close both flows!

Exactly that's why normally you only have one lever to turn on the other is temp

 

[Mike Jones Amber Hill]

So when the Lever is closed it can back fill because the hot and cold meet and mix before the lever closing.

In effect they are then in one pipe, and the one with the stronger pressure can push the other back down the pipe, or hold it at bay, stopping the hot having any flow to outlets.

This should not happen because a NRV acts as a barrier to stop back flow. If an NRV has failed it would allow the ba flow and this could be our problem?

We would need to isolate each mixer, and then turn on, one by one, to see when the problem returns.

Is that right?

It couldn't be an airlock in the pipes instead could it?

 

[ShaunCorbs]

Correct the nrv stops the back flow

Can happen depending on your mains water pressure eg higher than your hot

No you wouldn't get any water then

 

[Mike Jones Amber Hill]

Last question, any idea ballpark what it will cost to fix. I imagine it's a pain of a job as its a process of elimination and also access to isolation valves might be an issue

 

[ShaunCorbs]

Can't say due to it being a pain if the pipes are boxed in etc

You could do most of the donkey work eg finding the pipes making access etc

 

[Mike Jones Amber Hill]

Thanks for your advice, time to get someone in,

 

[Ben-gee]

If one of the bath mixers is playing up, I’d start there first.
Amazing how a thousand pound fancy tap can be brought to its knees by a 10p plastic nrv.