Super-heated hot water dilemma!

[SimonH]

Afternoon all, here's your central heating / hot water poser for the day....
We've got a gas powered Rayburn in the kitchen that heats our hot water in a tank upstairs. Our central heating is powered from a separate combi boiler in the cellar. The problem is that there doesn't seem to be any way of regulating the maximum temperature of the water, and even when the cooker is down to a very minimum the water seems to get ridiculously hot. Our power shower really doesn't like it and cuts out on a fairly regularly basis, I assume because the water is too hot. (The pump, and all others that I've seen, are only regulated up to a maximum temperature of 65 degC.)
I'm going to have a good look at the hot water tank to check how things are plumbed in but I assume that there is a pipe which travels through the cooker, heating the water within the pipe which then travels up to the tank and enters the coil within it, heating the surrounding water in the tank which is itself fed from a header tank in the loft. (Hope you're understanding this, I'm confusing myself! ) As far as I can tell there isn't any obvious way to regulate the maximum temperature other than turning the cooker down, but it's already on the very minimum temperature.
Anyone got any bright ideas?

[BUSHWHACKER]

Afternoon all, here's your central heating / hot water poser for the day....
We've got a gas powered Rayburn in the kitchen that heats our hot water in a tank upstairs. Our central heating is powered from a separate combi boiler in the cellar. The problem is that there doesn't seem to be any way of regulating the maximum temperature of the water, and even when the cooker is down to a very minimum the water seems to get ridiculously hot. Our power shower really doesn't like it and cuts out on a fairly regularly basis, I assume because the water is too hot. (The pump, and all others that I've seen, are only regulated up to a maximum temperature of 65 degC.)
I'm going to have a good look at the hot water tank to check how things are plumbed in but I assume that there is a pipe which travels through the cooker, heating the water within the pipe which then travels up to the tank and enters the coil within it, heating the surrounding water in the tank which is itself fed from a header tank in the loft. (Hope you're understanding this, I'm confusing myself! ) As far as I can tell there isn't any obvious way to regulate the maximum temperature other than turning the cooker down, but it's already on the very minimum temperature.
Anyone got any bright ideas?

Has you shower got hot and cold inlets?

[Sancho]

The method you describe is how most domestic hot water systems work so is probably right. Rayburns don't have a temperature control for the hot water, so you kind of get what you're given.

If you've got a modern cylinder, there should be a temperature control on it - i.e. it will close the feed from the Rayburn once it has reached a certain temperature (or something similar). If not, it will just kick out as much as you put in so you have to address the problem after the cylinder.

A thermostatic mixer on the shower should take care of the excess heat there if that's the only problem. Alternatively you could fit a TMV, feeding from the hot output of the cylinder and your cold water supply (probably the cold water feed into the cylinder), just after the cylinder to regulate the temperature. Should be quite easy. The only problem there would be that your water temperature may then not be as high as you'd like for your washing machine etc.

The 'correct' answer is to put individual TMVs all over the place, wherever you want a lower temperature (probably basin and bath with a thermostatic mixer on the shower). Still not a big deal if you can get to the plumbing.

The alternative is to put a large heated towel rail in your bathroom to dump some of the heat. If you have kids or elderly relatives, I would go for the TMV option to prevent any scalding risk.

[Wild Thing]

You really should have a heat bleed radiator on the rayburn system, with lockshield valves so that it can be set to take the correct amount of heat away from the cylinder and no one can tamper with it, system should also have a preasure release valve in it.

[andycook]

we have an oil fired rayburn

it does oven cooking (1 burner), hot water and central heating (2nd burner).
the hot water cylinder has a thermostat on it and is wired into the rayburns "ECU!", this is set around 65 degC.
a single drayflos pump - pumps water through the hot water cylinder and the radiators. BUT there are 2 electric zone valves one for hot water and one central heating, these are controlled by rayburn and thermostats, and direct the water flow

[SimonH]

Thanks for the replies everyone, think a thermostatic mixing valve (those safety things) is probably the best way forward. No little kids or old people at risk of scalding to worry about, but currently eating through shower pumps at a rate of knots, and it's all beginning to get a bit pricey!
Thanks again, Simon

[fatfires]

I think you need to check the operation of the thermostat in your rayburn also see if you can adjust (or have it done by someone who knows) your low gas rate, sounds more like a servicing issue/faulty stat to me
how many burners does your rayburn have
was it originally gas
are you on nat gas or LPG
is the system gravity or pumped, direct or indirect
the more info you can give, the more answers you can get
PM me your landline number - I'll give you a bell
(I am known as a heating engineer)

[SimonH]

Thanks for all your replies, it looks like the TMV is the way to go.
Just out of interest, I've drawn a little doodle of the plumbing around my hot water tank, I can't see a pump to move the hot water from the Rayburn to the tank, I'm guessing it's a convection type system where the hot water finds its own way in an upward direction towards the tank...... or is that a ridiculous suggestion?

1=hot water (to heating coil) in
2=hot water (from heating coil) out
3=heating coil vent?
4a=hot water out to taps in bathroom
4b=hot water out to shower pump
4c=hot water vent?
5= cold water supply (presuming to fill the tank, comes from cold water tank in loft)
6=shower pump hot water out
7=shower pump cold water out
8=shower pump cold water in (from large tank in loft)

It looks like the best thing is to put a TMV from the hot supply to the shower pump but my other question would be.... is there a pump I should be able to see that circulates the hot water from the Rayburn? Thanks in advance, Simon

P.S. Fatfires, thanks for your offer, I'll PM you my number

[BUSHWHACKER]

Thanks for all your replies, it looks like the TMV is the way to go.
Just out of interest, I've drawn a little doodle of the plumbing around my hot water tank, I can't see a pump to move the hot water from the Rayburn to the tank, I'm guessing it's a convection type system where the hot water finds its own way in an upward direction towards the tank...... or is that a ridiculous suggestion?

1=hot water (to heating coil) in
2=hot water (from heating coil) out
3=heating coil vent?
4a=hot water out to taps in bathroom
4b=hot water out to shower pump
4c=hot water vent?
5= cold water supply (presuming to fill the tank, comes from cold water tank in loft)
6=shower pump hot water out
7=shower pump cold water out
8=shower pump cold water in (from large tank in loft)

It looks like the best thing is to put a TMV from the hot supply to the shower pump but my other question would be.... is there a pump I should be able to see that circulates the hot water from the Rayburn? Thanks in advance, Simon

P.S. Fatfires, thanks for your offer, I'll PM you my number

Shouldn't the cold feed to the shower be mains pressure?

[SimonH]

Bushwhacker, you raise a very good point, I've tried to trace the cold supply all the way back to source and the closest I can find is that there is a pipe that seems to come out in the loft at pretty much the same point that the pipe disappears up into the roof from the airing cupboard. I've assumed that it's the cold supply but it definitely seems to come from a large tank in the loft that fills pretty quickly. Our water mains pressure is ridiculously high (we live down the hill from the water main in the road) so perhaps having the shower supplied from a header tank was the best way to try and have equal pressures in the shower before the advent of power shower pumps? If it were a tank for the hot vs mains for the cold the cold water would shoot into the hot tank or just not allow any hot water to come out?
Think I need to give up the day job and become a plumber, it seems like a dark art at times!

[fatfires]

Shouldn't the cold feed to the shower be mains pressure?

no, not in this case, mains feed to instantainious electric shower heaters yes but equal pressure in gravity (before the pump) fed systems i.e. cold feed to cylinder from tank gives HW pressure = cold feed to pump (less if you realy want to be pedantic like some on here are sometimes any frictional losses associated with the resistance of the cylinder and associated supplies)
Mains fed systems inc. cylinders are a whole different ball game though!
I know I make fire balls now but am a heating engineer by trade

[Sancho]

Simon, the tank is most likely there to prevent back-siphonage into the water main from the shower. That's how they used to do it in the good old days. Have a look inside and you will probably find a squirrel or pigeon. Lovely.

It is also possible that your house previously had low pressure, the tank was installed to provide enough for the pump to work and the main was subsequently upgraded.

There may well be a pump on the hot water cylinder that delivers hot water at mains pressure to tie in with mains cold. To be honest, it is almost impossible to make any useful suggestions without seeing the system, but Fatfires should be able to help you if you describe it over the phone. If you know a plumber, tease them in by asking for a quote for the work and get them to work it all out for you.

Most Rayburns don't have a thermostat for the hot water, but check.

[plumb bob]

Power showers require hot and cold feeds direct from tank, not mains.

One other option is to fit a 28mm zone valve on the gravity flow ( after the open vent) and a cylinder stat, comonly known as the C-Plan.
This will give you thermostatic control over your entire hot water system.
Cost of parts about £100.00

I would also have a specialist check the AGA for faulty thermostat and make sure it is properly serviced at least once a year.

[Sancho]

Power showers require hot and cold feeds direct from tank, not mains.

Why's that then? To stop nasty pump pollution getting in their precious water supply? Maybe they could think about blocking up all the holes in the main...