Hot water not so hot

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Our hot water is not so hot. Previously we could run a full bath of hot water with no problem. Now, after about 30 seconds, the water begins to run tepid.

We have an indirect water system with gas central heating run by an Ideal Classic RS250 boiler. The central heating still works.

The set up of the hot water cylinder is that instead of a cylinder thermostat, there is a TRV on the pipe going into the heat exchanger coil (wired to a detector on the outside of the cylinder). The flow pipe from the boiler and return pipe are on the top of the cylinder rather than the side. The pipe going into the coil is boiling hot so it should be heating all the water in the cylinder.

I can't find a three-way (or even two-way) valve anywhere so I'm assuming we don't have one. Basically the timer in the airing cupboard has to be on to give us hot water and central heating. It's one of those simple dial jobbies with trip switches which have "on until B", "off until C", "on until D" and "off until A" If we don't want CH then we just turn off all the radiator TRVs.

Until the problem happened we had the thermostat on the boiler set to 3 (the recommended summer setting - I'd forgotten to increase it for the winter) and the TRV on the hot water cylinder set to 6 or 7. The actions I've done since are to increase the boiler thermostat to 5. I've bled all the radiators as well as a couple of bleed valves on the pipes going into and out of the hot water cylinder coil. There is a slight drip from the hot tap in the kitchen which needs fixing but I don't think this has any bearing on the problem as it didn't start at the same time as the tepid water.

An amateur plumber friend suggested there may be an airlock in the coil and suggested turning off all radiators, turning the hot water cylinder TRV to max and leaving it an hour or two - he thought this would blast the air lock out. Unfortunately, it didn't work. Other than the initial lot of hot water being hotter than before, it soon settled down into its tepid state. My friend also suggested that it may be due to a failed thermostat inside the hot water cylinder, although I wasn't aware there was such a thing. Maybe I misunderstood him and he meant the thermostat on the outside of the cylinder.

Does anyone have any suggestions?
 
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check that the small tank in the loft has water in it.
 
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OK, I've checked the small tank in the loft. It's about a third full of water - pretty sludgy water at that. I've not put any Sentinel in myself but there is an empty container by the tank which suggests the previous owner did. This could be close to ten years ago.

I can take the head off the TRV but I'm not sure what I need to do. Note that there's a wire leading out the back of the head to a detector which is strapped towards the bottom of the hot water cylinder.
 
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I can take the head off the TRV but I'm not sure what I need to do. Note that there's a wire leading out the back of the head to a detector which is strapped towards the bottom of the hot water cylinder.

under the head there is a pin which should move up and you should be able to push it down

if its not stuck :idea:
 
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read the topic and thought to myself

yeah it is pretty overated isnt it :D

Try telling my missus that. She has her baths deep and the water hot enough to lift the skin off your body. :LOL:

The pin in the head is fine - spring loaded and pushes in and out. The pin in the body I could only move with pliers. There doesn't seem to be a great deal of movement in it between fully open and fully closed but I assume this is right. So I've left it pulled out fully and put the head back set to MAX.

But then - separate issue - I noticed that I couldn't hear the boiler. I had adjusted the thermostat on it to its winter setting (between 5 and 6) a few days ago. When I turn DOWN the boiler thermostat it only fires up and stays fired up on just above 3 (max is 6). Why would it not stay fired up on higher settings? Is it jut because it only needs to heat up the hot water at the moment as all the radiators in the house are switched off (i.e. set to 0)? If I switch on all the radiators will I then be able to have it fire up on a higher setting.

And by the way, is the expansion tank fine or should I chuck some Sentinel in there?

Thanks
 
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try taking the tap stat head off and leave it off.

is the an air vent ot the coil?
 
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It sounds as if your system may not be correctly configured.

If you have a Drayton TRV style valve on the cylinder coil then that is designed for a pumped system.

Unless you have TWO pumps (?) then there would be no way to turn off the central heating.

Could you have two pumps and one has failed? That would be unusual though.

The usual arrangement would be one pump and a motorised valve to turn off the heating.

Tony
 

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I would be looking for possible blockage at first tee on the return or flow pipe at the cylinder
 
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Here's a photo of the pipes at the top of the hot water cylinder. I've since taken the tap stat head off. I've also bled the vents from the flow and return pipes (the two bits sticking up). The flow pipe (the one on the left) is boiling hot all the way to the top of the cylinder. The return pipe is cold. After leaving it all afternoon, running the hot tap produces a bit of warmish water and then it runs almost cold. So it tends to suggest an airlock or blockage - am I right? If so, what's the best way to clear either or both? And what could be causing a blockage - just general sludge in the system?

plumbing005.jpg
 
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christ a micraversion :eek:

haven't seen one of those for 20 year or so :D

could well be full of carp

just a thought did you close the valve when you bled the air

might be worth a try :idea:
 
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I presume you mean bleed with the TRV/top stat closed. I didn't but I have done now. Didn't seem to be any air coming out though - how long should I bleed it for though? Anyway I'll see if that makes a difference. And if there's gunk in the system how do I clear it out - inhibitor, flushing or drain the whole system?
 
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Just to the right/underneath there is a bypass lockshield valve.

I dont suppose you have touched it lately have you?

Regardless, count the number of 1/2 turns needed to close it and if more than two the reopen it by just one full turn.

But for testing, fully close it and see what effect that has!

During all this you should have been feeling the two pipes to measure their temperatures, The flow should be about 70° and the return about 10° lower.

Tony
 

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