Hot Water Timers

[Mr. Dazzle]

I think my hot water timer might be on the fritz.

The hot water ('old style' separate boiler and tank system) comes on, but then it doesn't seem to switch off. The boiler just stays on. It doesn't do it every time, so the only way we know it's happened is either by noticing the sound of the pump or when you find the hot water is bloody boiling!

We've already had a man out and he's replaced the electronically actuated valve - which was clearly dead TBF - but that's not fixed it. In classic style the problem didn't manifest itself when he was here. If you switch the hot water on/off with the control panel nothing much happens after it initially switches on. It just stays on. The only way to turn it off is at the boiler itself.

I'm thinking maybe the timer is caput? Intermittent fault screams electronics failure to me?

My question is though, can I just buy a new timer and stick it on? Is it that simple? It's one just like this. Until very recently I didn't realise they just clip onto the panel and they have a multi pin connector on the back. I'd never looked

https://www.screwfix.com/p/drayton-lp52 ... lsrc=aw.ds

[Le_Fromage_Grande]

Sounds like the thermostat in the element is fucked, it'll burn the element out eventually, either way it's a new element, not difficult to do, just a bit of a ball ache if you have to disassemble the airing cupboard (like I do) to get the element out.

The thermostat is probably a bimetal strip btw.

[Mr. Dazzle]

But why would that mean the pumps and boilers don't turn off?

My understanding is - and this is based on nothing more than pondering how the whole thing works and looking in the cupboard - the timer says "let's have some hot water then!" and tells the boiler and pump to switch on, then opens the valve which means that hot water the boiler produces flows through the hot water cylinder. That hot boiler water heats up whatever is in the tank until either a) the time tells it to stop or b) the thermostat in the tank realises the water is to hot and issues an 'overide' command.

When the timer turns off again it shuts the valve to the tank, then tells the boiler to turn off. The boiler carries on for a couple of minutes with it's own self-determined cool down period then switches itself and the pump off.

So if the timer ain't telling it to turn off it'll just stay on forever / until the safety systems kick in?

Or not?

Dunno!

[Le_Fromage_Grande]

Sorry, I misunderstood what you meant, I thought you had an electrically heated hot water tank, when referring to something as "old style" please remember how old some of us are - to me it means a back boiler and immersion heater, not a fancy gas central heating system

I'd have thought the decision to heat the water would involve measuring the temperature of the water, not just heating it up every x minutes.
I've never had a heating and hot water system like yours (yes, I've never lived in a house with radiators) but when people at work have had a similar problem it's been the valve that decides which way the hot water goes which has been faulty

[KungFooBob]

I work for a company that makes HVAC controls, Thermostats, Diverter Valves, Pumps, Programmers, etc..

But I work in IT so I have no idea about the products and how they work.

HTH.

[Mr. Dazzle]

"old style" please remember how old some of us are

Yeah fair enough

It's the latest 1980's concept!

had a similar problem it's been the valve that decides which way the hot water goes which has been faulty

And that was replaced first. I think it's safe to assume at this point that you know even less about these systems than I do

[KungFooBob]

BTW, don't get a dumb control, Smarthome is the future!

[Mr. Dazzle]

BTW, don't get a dumb control, Smarthome is the future!

We've got Smart Metres for gas and electricity.

The damned thing is smart enough to report how much gas we use to the gas company, but not smart enough to show us the same info on the little tablet thing that comes with it. The bloody snitch.

[Kneerly Down]

If the boiler is staying on when both the hot water and central heating are supposed to be off it's almost certainly your controller.
I don't know why your plumber thought it was the mid-position valve (if it's not 2 2-way valves) would cause that...that's if your hot water is getting hot in absence of calling for it while the CH is on or vice versa.

I'd try the new controller on the existing plate assuming they do indeed match*


* Well, I say I would. When I had the same issue, because it's a 130 mile round trip to a store that sells, them I rigged-up a 'temporary' solution....13 years ago!

[Mr. Dazzle]

There are three valves - upstairs, downstairs and hot water. All of them are just 'on/off'. Plus an automated bypass valve for when all three are off.

So the original Q...shall I just buy a new unit then?

[Hairybiker84]

Very likely to be the programmer. Both the hot water and central heating outputs from it are via volt-free contacts of internal relays. I've had them in the past where the relay latches in even though the light that should be an indication of whether the relay is energised or not is out.
If its a standard programmer they normally fit a standard base with wireable terminals in the base. The programmer clips in at the top and hinges down to make contact with the terminals. Usually retained by a small screw on the lower edge.

[Mussels]

There's a thermostat on the side of your tank which should tell the controller when to switch the boiler off, try tuning it right down to see if it makes a difference.
I'm assuming you don't have central heating on at this tme of year so unlikely to be a stuck valve, only reason it would be that is if you were trying to heat the radiators and it was sending hot water through the tank instead.
I'd go for controller or tank thermostat.

[Mr. Dazzle]

The valve was clearly knickered anyway, so I'm not too bothered that it's been changed.

I'll nip to screwfix and get a new programmer. It'll cost less than the plumber call out

[Le_Fromage_Grande]

"old style" please remember how old some of us are

Yeah fair enough

It's the latest 1980's concept!

had a similar problem it's been the valve that decides which way the hot water goes which has been faulty

And that was replaced first. I think it's safe to assume at this point that you know even less about these systems than I do

Well obviously, but it's still fun having a guess

[Nobby]

The Programer is a Switch , which powers the Stat , which powers the valve, which moves a bit then switches the Boiler and pump(s)
If the Boiler is staying on , then either the Stat or valve is stuck.

[Silly Car]

My guess is the thermostat on the hot water tank is kaput.

Ours has two settings, an automatic anti-legionnaires setting which raises the temp to above 60 degrees(?) every 7 days and a normal setting which we control. The anti-legionnaires setting triggers every time the power to the boiler is restored irrespective of the timer control.

[snip] What Nobby said…

H’actually, if the boiler internal stat is set below hot water stat temp, the tank stat (especially on legionnaires setting) will permanently call for heat.

[Mr. Dazzle]

TBF there's not much left that it could be....

I've just had a look and I've decided I'll start with the programmer on two grounds;

a) I want to get a 7 day one anyway, rather than the 24hr one that's there now.
b) To change the thermostat I'd have to drain the hot water tank (it's at the bottom, I just looked). That's way more effort

[KungFooBob]

Your tank thermostat is in the tank?

That's novel, they're usually just tied on with wire.

[Silly Car]

Mine is fitted to a dry tube into the bottom of the tank, three grub screws and it slides out.

EA594EC6-1019-47F0-9D60-7AC520CB52FB.jpeg (44.53 KiB) Viewed 495 times

[Mr. Dazzle]

I will not claim to have looked in great depth

It's got a Honeywell box about a quarter of the way up, screwed/bolted to the outside of the tank. It's also got a bit of springy wire almost like a washing line looped around it and the tank, the box has a groove which the wire sits against.