Immersion heater not heating water, AGAIN!!!

[DeanR32]

Morning PH

I've got another problem with my hot water again. It's supposed to heat overnight (as you know), but in the morning it's like warm at best.

During the evening over the weekend I set the timer to heat up so I could see if it gets hot at all. I started beating the water, and 10-15 mins later, it started running through the tundish luke warm.

I'm away at the moment for work, so my missus called a plumber to come poke about. He set the water to heat as normal, through the night, and called my missus to ask if was hot. Of course it wasn't, so he said he will order a new thermostat and fit it Monday.

Is he right? He said the water is getting way too hot and getting released through the tundish, but it was only luke warm when I felt it. It could only have been heating for 15 minutes max.

Any suggestions from the knowledgeable fonts on PH?

[dirkgently]

I would look at the expansion vessel or air bubble (dependent on make of cylinder).

[Dave_ST220]

Water should only be in the tundish if the PRV operates, luke warm water shouldn't cause that so sounds like the PRV is letting all the water drain away?

[bomma220]

Dave_ST220 said:

Water should only be in the tundish if the PRV operates, luke warm water shouldn't cause that so sounds like the PRV is letting all the water drain away?

Yes I agree with this, the PRV shouldn't be passing lukewarm water. Worth getting the PRV checked before anything else.

[DeanR32]

Cheers for the replies

We have had a problem with the expansion vessel before. A couple of months ago it was full of water. A pal of mine (qualified) emptied it. When I checked it (Sunday) it was still as light as it was when he emptied it.

I'm certain the water is starting to heat, but something is letting it release through the tundish luke warm.

Does this shed any light a bit better?

[bomma220]

DeanR32 said:

Cheers for the replies

I'm certain the water is starting to heat, but something is letting it release through the tundish luke warm.

Does this shed any light a bit better?

The only thing that could do this would be the PRV, can you get your pal to check it?

[bstw]

DeanR32 said:

Cheers for the replies

We have had a problem with the expansion vessel before. A couple of months ago it was full of water. A pal of mine (qualified) emptied it. When I checked it (Sunday) it was still as light as it was when he emptied it.

I'm certain the water is starting to heat, but something is letting it release through the tundish luke warm.

Does this shed any light a bit better?

I'd get the expansion vessel changed, they're only about £30. If it's filled up with water it's possible that the diaphragm is shot.

[DeanR32]

Cheers again for the replies

As there was a problem with the vessel, I think I'll get that changed anyway. My thought was that it was a faulty PRV, but there can't be much that could go wrong with that, surely?

[bomma220]

DeanR32 said:

Cheers again for the replies

As there was a problem with the vessel, I think I'll get that changed anyway. My thought was that it was a faulty PRV, but there can't be much that could go wrong with that, surely?

Good idea to get that done, a PRV can fail tho'. Think of a broken coil spring on a car, can cause a whole lot of

bother for a simple fault. Wish you all the best with getting the problem sorted mate

ps And don't call me Shirley

[RammyMP]

I'd change the vessel, ours is the same as yours and about 3 weeks ago the expansion vessel split in the middle of the night and flooded the airing cupboard. For £30-£40 I'd change it. You can do it yourself, just check the pressure of the tank before and after fitting.

[Rickyy]

If the vessel has failed once already, the PRV is probably shot. Once they have been operated, they usually get crud on the valve face and don't hold pressure anymore.

The water warming up is probably causing just enough of a pressure rise for the PRV to start passing.

I'd replace the PRV and the vessel.

[dirkgently]

Rickyy said:

I'd replace the PRV and the vessel.

Spoken like a plumber.

[anonymous-user]

DeanR32 said:

We have had a problem with the expansion vessel before. A couple of months ago it was full of water. A pal of mine (qualified) emptied it. When I checked it (Sunday) it was still as light as it was when he emptied it.

What exactly do you mean by that?

There are two pressure relief valves. One is a combined pressure & temperature relief valve, situated at the top of the cylinder, whilst the other is on the cold water inlet side, often combined with the pressure reducing valve assembly. Do you know which one is leaking?

Either valve will only be letting through a small amount of 'expanded' water, so if the immersion heater is working correctly then the cylinder contents will be hot. If the water from the hot taps is only lukewarm, then this suggests that the immersion thermostat is kaput. Can you tell from the electricity meter 'spinning disc' just how long the immersion heater is actually operating?

Many would advise against DIY work on unvented cylinders. It is indeed not 'rocket science', but regulations do exist...

[Dave_ST220]

280E said:

It is indeed not 'rocket science', but regulations do exist...

It can be if done wrong

[Lewi25]

Hot water running through tundish would indicate an issue with the temperature & pressure relief valve wouldn't it?