expensive luke warm baths - help!!!!

[Simon]

Hi all,

As you can probably tell, I know next to nothing about plumbing, DHW systems etc, so apologies in advance...

I think I have a conventional indirect CH and hot water system - ie gas boiler heats primary water source which is pumped through a coil in the water tank thus heating the secondary water source and feeding the primary water through the CH system of radiators around the house.

The hot water has an electrical "top up" system on the tank in the attic. This appears to be jacketed heating element in the tank which has no thermostat. There is an on-off switch (but no timer) to the supply. There is no thermal cut-out built in.

Emerging from the tank is a pipe which has a TRV fitted. I presume this controls the water heat (or flow?) to the CH system? To be honest I'm not really sure what this does, and would be grateful if someone could clarify it for me or link to somewhere on the web.

The problem I have is that it seems to take a long time to heat up the hot water for a bath, and it is not that hot when it runs. I have re- lagged the tank recently, and this seems to have made a difference in that I can hear the water in the tank getting hotter quicker and bubbling away. The pipes certainly seem hot enough, but when I run the taps the water comes out lukewarm.

I presumed that using the gas boiler to heat the water in the tank would be best and then topping up the heat via the electric water heater would offer the most efficient and/or economic means of getting the hottest water at the least expense.

But how would this be affected by the setting on the TRV of the pipe emerging from the tank? What does it do and what setting would be best?

I presumed that if I turned off the radiators or had them set low that this would result in the water circulating through the pipes at a higher temperature and hence there being more heat for the DHW. Is this right?

What about the radiator in the bathroom? I have read that this should always be on max. Is this right? If it isn't on max, will this affect the water temperature?

Sorry for the all the questions. Any help or understanding you could give me would be great. At the moment I'm adjusting various things based on little more than guesstimates and (unsurprisingly) this approach hasn't worked.

Many thanks for reading this far and for any help, insight or advice you are able to give.

Simon

[dennis]

Your description doesn't make sense to me.

Has it always been like this or is this a new problem?

Heating it all by gas would probably be cheapest. I don't understand why you have the electric heater in a tank in the attic, is this the same hot water tank the boiler heats?

Are you sure its a TRV? Could it be a mixing valve with hot and cold in and mixed out?

Is this a pumped system with any sort of motorised valves or multiple pumps?

If you have a camera you could post a few pics, they can be useful for identifying components.

[Simon]

hi. many thanks for your reply.

some photos of the hot water tank, the TRV (if that's what it is) and the electric heat element which are all in the loft. The boiler (downstairs in the kitchen) is an old Baxi. If the photos are no use let me know and i'll take some more, or some of specific elements.

once again many thanks

Simon

[Tabby]

Doesnt sound good

Odd, a pic could help

If its bubbling then its boiling. It should never get that hot. I certainly hope its a metal tank, not plastic.

Cheapest is to use gas always. Electric heat costs 3-4x as much per given amount of heat. I'd switch the electric element off and leave it off.

We need to know what your setup is, some aspects of it sound odd. Lots of pics might help.

no

no

Well, we need to know what setup you've got really. It sounds like nothing can be assumed.

NT

[Simon]

hi. many thanks for your reply.

house is about one hundred years old. i don't know if the setup is unusual or not.

so if i use only the gas boiler to heat up the water, does it make a difference whether any of the radiators are on or off?

Simon

[Andy Dingley]

WTF is a TRV doing there?

I think you need one of either three things:

• A plumber, on-site and looking at it

• A good schematic diagram of what you have, weird-ass TRVs and all, so that we can see the system layout.

• Your own copy of Treloar's "Plumbing" (top book) and an evening's reading. It's not rocket science, but untangling past bodgeries can be very hard work as they don't have to follow any rational plans.

[John]

hi. many thanks for your reply.

house is about one hundred years old. i don't know if the setup is unusual or not.

so if i use only the gas boiler to heat up the water, does it make a difference whether any of the radiators are on or off?

Simon

That TRV is wrong. The only time I have come across anything similar is a valve that it operated by a sensor on the tank to close off the flow to the inner coil when the water gets up to temp - nowadays a motorised valve would be used.

[Terry Fields]

I'm fairly sure it's a capillary-type control for the hot water. There should be a thin pipe connected to a sensor which is held to the hot water tank by an elastic strap.

The sensor my have fallen off (or been taken off) or be incorrectly placed.

The OP should check if the capillary tube is in place and undamaged, the sensor is in place (half way up the tank) and that it is set to a suitable number (ours was set on 5 for water about 65 degC). Googling the makers name (if visible) might turn up more info.

There are more modern (read: more complicated) ways of achieving the same end.

TF

[Malcolm Gray]

Ahve you got any sort of mixer either on or under the bath (I know some systems use one to reduce the hot temperature as a safety feature)

[Dave Liquorice]

The components of that system look quite old... Maybe it is a thermostatic valve with a remote sensor on the tank, it's difficult to tell from the pics. Or perhaps the orginal valve with remote sensor failed and someone, incorrectly, replaced it with one that would be used on a radiator.

I think it is safe to say that this system is a bit "odd". Best bet is for the OP to spend a while working out what is connected where and draw it out.

[Simon]

if this TRV is being used to close off the flow to the inner coil when the water gets up to temp, then the best thing would be to put it on max, then at least the gas boiler would be heating the water tank to the max of the system's capabilities? I'll try that tonight.

Does having the radiators on or off have any effect on the time it takes the boiler to heat up the water or the temperature it will heat up to? I had always presumed that if you had the radiators on they would take some of the heat out of the pipes, so that the water circulated around the CH would be (and hence through the coil) would be slightly cooler than otherwise and hence would not be heating the water tank to the same degree. Is this right or wrong?

[ARWadsworth]

I could not decide if it was a TRV.

If it is then it must be used as a form of frost protection system.

It could be a pressure reducing valve. The photos were not very clear.

[Roger Mills]

I'm struggling to work out what sort of system you've got! Sharper pictures may help a bit - but even they wouldn't tell the whole story 'cos we can't see what's hidden under the insulation.

When I read your first post, and before seeing the photos, I thought you had probably got a gravity HW and pumped CH system, with a Drayton Cyltrol valve or similar on the primary return from the cylider. A Cyltrol is a bit like a TRV, but it senses the return flow temperature (which rises as the secondary water in the cylinder gets hotter) and cuts off the flow when the DHW gets hot enough. I had a setup like that in my previous house over 30 years ago. Just occasionally, the water would circulate the wrong way round the gravity circuit such that the Cyltrol then sensed the *flow* rather than *return* temperature - with the result that we had tepid hot water. I don't think it's relevant in your case, but I've written it anyway, just in case it inspires anyone else to do a bit of lateral thinking which *may* be relevant.

I suppose that the 'TRV' in the photo *could* be a variation on a Cyltrol - but it looks more like a radiator-type TRV, to me so I don't know what it's doing there. Also, if you had a gravity HW circuit, I'd expect to see 1"/28mm pipes rather than 1/2"/15mm!

Can you tell us a bit more about the components in your system. How many water pipes are connected to the boiler? Where is the pump? Does the pump run when *just* the HW is switch on, or does it only run when the CH is on? Are there any motorised valves anywhere? If so, how many, and what type - 2-port or 3-port?

[Roger Mills]

There's no simple to that question! It depends on the capacity of the boiler, and of the pump, and of the cylinder to absorb heat. In the unlikely event that it's a modern fast-recovery cylinder which can absorb the boiler's full output, the water will get hot fastest if the CH *isn't* on at the same time. But if the cylinder can't absorb heat very quickly anyway, it probably doesn't make much difference.

[tony sayer]

So it does got one like that 'ere I bet its got stuck closed;!...

[Andy Dingley]

Hard to say. If you're boiling the tank (from the noise) and the hot water is not only slow but also luke-warm, then the only conclusion would seem to be that a mixture of hot and cold is being drawn off into the hot delivery pipe. Maybe the draw-off is mounted too low-down on the tank?

The TRV could be there to control the primary circuit heating the tank, but there are two problems there: TRVs are too small bore to use on a delivery, or especially a primary circuit. More importantly, it's sensitive to air temperature, not tank water temperature. Is there any bypass circuit to the TRV? If it's _supposed_ to supply hot water to the bath, but it's throttled by its diameter, could the bath hot supply be pulling cold from somewhere as well?

[Tabby]

Your photos are a handy start, but they dont give nearly enough information to know what type of system you're running. 2 things would really help:

1. a clear picture of every element of the system.
2. Given that it looks like this may be a weird setup, the only way to be certain of whats going on is for you to trace every pipe to see how its set up. Short of that, the more info you can give us the better.

I think though that we can say that a boiling tank plus lukewarm hot feed probably does equal an odd system.

NT

[Simon]

Thanks everyone for all your advice. Tomorrow morning (its too dark up there now!) I'm going to take some more photos and try to make these clearer than the previous ones. I'm also going to take the lagging off the tank so you can see exactly what there is underneath. I seem to recall there being a thin pipe held on to the tank from when I put the lagging on, so maybe Terry is on the right track when he says: "I'm fairly sure it's a capillary-type control for the hot water. There should be a thin pipe connected to a sensor which is held to the hot water tank by an elastic strap."

But once the lagging is off and I post up some decent photos I'm sure the system will be revealed in all its glory!

Once again, many thanks to you all for your time and expertise. It is really appreciated.

Simon

[Terry Fields]

I'm going to make a guess that your system is the same design as the one we used to have: boiler heating water in the combined primary circuit (with coil in the tank) and the CH side. DHW is obtained from the heating effect of the coil. A red-handled gate valve allows primary hot water through the CH system. DHW temp is controlled by a capillary thermostat, that shuts off the primary flow to the coil when the correct temperature is reached. There's an immersion heater for backup. Somewhere there will be a pump bypass loop for when the capillary valve shuts with the CH shut off.

It sounds to me like the capillary valve, either through the setting or some fault, is turning off the primary flow to the coil at too low a temperature, hence the lukewarm water. The boiling sound is probably the primary water being heated too high, due either to too high a thermostat setting on the boiler, or a fault with it.

Try turning down the boiler stat to about 2/3 of max, or try turning it down to see if it clicks off when the bubbling sound starts, and set it below that level. Turn up the capillary valve setting to 2/3 max (screwed out) and see if the water gets hotter. Failing that, open it fully. Be careful when testing the DHW.

I regret to say i can't remember the maker of our capillary valve, but it looked identical to yours.

TF

[Tabby]

I think whatever's happening the boiling's probably caused by the immersion heater. Its possible but not likely for a gas boiler to boil a tank of indirectly heated water.

NT