Central heating continuously runs

[Daren Friday]

Hi

We have a Potterton Suprema boiler, a Potterton EP3002 wall timer and a Wickes wall thermostat.

The heating switches on OK according to the timer schedule but fails to switch off when it reaches the right room temp set on the thermostat so we just get hotter.

I had to have a new thermostat for some reason but I seem to remember there being 3 wires into the stat but there appears to be only 2.

Is that right? And would the missing wire be the one to turn off the heat?

(Pictures attached)

Thanks

Daren

+-------------------------------------------------------------------+ |Filename: Boiler.JPG | |Download: ||Filename: Stat.JPG | |Download: ||Filename: Timer.JPG | |Download: |+-------------------------------------------------------------------+

[Stormin Mormon]

Most likely, two wires is how it was designed. Third wire could be anything, but probably a common.

It's possible the thermostat isn't the problem. I'll copy in the alt hvac group, they field this question often.

Christopher A. Young Learn more about Jesus

.

Hi We have a Potterton Suprema boiler, a Potterton EP3002 wall timer and a Wickes wall thermostat.

The heating switches on OK according to the timer schedule but fails to switch off when it reaches the right room temp set on the thermostat so we just get hotter.

I had to have a new thermostat for some reason but I seem to remember there being 3 wires into the stat but there appears to be only 2.

Is that right? And would the missing wire be the one to turn off the heat?

(Pictures attached)

Thanks

Daren

+-------------------------------------------------------------------+ |Filename: Boiler.JPG | |Download: ||Filename: Stat.JPG | |Download: ||Filename: Timer.JPG | |Download: |+-------------------------------------------------------------------+

[Steve]

The stat should only need 2 wires if its got batteries in it. The pictures are of such small size and poor quality, I can't tell much else. Its possible that you have been having this problem since you put the new stat in.... most likely because the anticipator setting isn't correct, or the temperature delta isn't set correctly, or both.

[Stormin Mormon]

I'm sure the professionals on alt havoc will help.

Christopher A. Young Learn more about Jesus

.

I've tried 2 other types of stats and all have the same result, the heating ignores them when room reaches temp. I've just changed the stat for a Honeywell CM900 and again I get exactly the same result. If I move the slider to off on the EP3002 everything closes fine.

I thought maybe I'd wired the stat wrong so I rewired it and now I've popped the motorised valve (Myson Power Extra MPE228).

I've ordered a replacement valve and EP3002. See how we go?

+-------------------------------------------------------------------+ +-------------------------------------------------------------------+

[Bennett]

[Steve]

Keep playing with it, keep breaking and changing parts... you'll eventually change something and accitentally "fix" it, *OR* you can call you local Master Tech and get the problem corrected the first time and be done with it.

[trader4]

Yes, or a short in the wiring. Should only take 2 wires to do the control. A third wire is typically used to provide additional functionality, like power so the thermostat can be lit up, etc.

And what is the history? Did it ever work? Was it working and then something was changed?

Also the overall settup isn't clear. In these parts we usually don't have seperate timer and thermostat. We have a programmable thermostat that combines temp settings for various periods with a clock.

[Bill]

Not everyone has an instant-gratification fixation. I'm sure you could troubleshoot it faster, but as long as he is being safe, give the man a little credit for trying! I do!

[RBM]

My condolences, I've never heard of one, but a Google search seems to indicate it's the lemon of all boilers. Do a search, there are plenty of help sites, as it seems that everyone that owns one of them has problems

[The Daring Dufas]

Years ago in the TV repair business we called them "Tube Changers". ^_^

TDD

[Bill]

I recall a tube tester at my local drug store, but I am a little young to remember the big picture. Was "Tube Changing" frowned upon back then (mid-late 60's?)? We always wore out the dials--we were quick! : )

>

[Steve]

Thats been my point all along for HVAC systems... A good tech can diagnose the system, show you what the problem(s) is/are, correct those problems with parts from his well stocked service truck, and warranty those repairs ..... usually for 1 year.

[krw]

Ha! A good repairman could take the make, model, and symptom, and tell you exactly which part failed and it's value or tube number. I worked for a guy like that.

There's nothing wrong with the technique.

[AaronL]

I worked TV repair in the late 50's. My recollections:

People tried to save money fixing their own TV sets by using those drug store tube testers. Trouble was those tube testers often said a good tube was bad thus wasting the money the customer was trying to save by not calling a TV repairman.

Tube changing (that is trying a new tube in place of a suspected bad tube in a working TV) was the quickest and most reliable way to see if that was the problem. There were specific tubes that did specific things so you didn't have to change out the whole TV's tube set. For example if the vertical hold wasn't locking there were just a few tubes that could cause that and you tried only them.

We didn't carry schematics for all TV models in the shop. They came in a packet with other info on the particular set and were expensive. A good tech could fix most TV problems without one. Tube TV's were incredibly simple and easy to work on compared to today's electronics. If we couldn't fix it without a schematic, then of course we ordered one (at the customers expense of course) and then put it in our library for future use.

We mostly used a VTVM (vacuum tube voltmeter) and a scope in the shop. For service calls we carried VOMs (volt ohm meter) and a picture tube tester along with a case of replacement tubes.

The majority of sets were fixed in the customers house. (Most TVs were very large and heavy in those days so we usually went to the customers house.) If the set couldn't be fixed by tube swapping then it went to the shop to fix. When repaired we delivered it back to the home.

Yes we swapped boards in mainframes at GE in the 60s also. Like tubes swapping out was a quick method of troubleshooting.

[Bill]

You are fortunate that you can do the work for yourself, and don't have to rely on locating a good tech. As we have discussed before, the waters are treacherous!

[Scott Lurndal]

Hmm. A number of sets that I worked on in the 70's had the schematics glued to the inside of the case.

In this case it was past midnight, testing a completely new firmware and OS on a working customer mainframe and the FE had gone home hours ago. Given the failure was in a Load Index Register instruction, which was handled by the Fetch module, I tried to swap the two (20"x30") fetch cards with the on-site spares kit. The new OS still faulted. Tried the two Execute Module cards. Still faulted. Eventually got around to swapping out the MCW (Memory Controller Write) card which fixed the problem. All night, alone in the datacenter of one of Belgiums larger banks. Probably wouldn't happen nowadays.

[AaronL]

You may be remembering the chassis tube location diagrams that were glued inside the cabinets of most sets. Very handy since many tubes required some physical contortion on the tech's part just to reach them in an inaccessible part of the cabinet (when in the customers home). Also they gave the tube type (6AU6, 6V6, ect) by which you could locate and swap the tubes you suspected of causing the problem.

Further a schematic *glued* inside a cabinet would be of little use in the shop since after removing the chassis it was put on the bench to work on and the cabinet was stored in the back of the shop.

But I can only speak for my 50's experience. Your 70's experience may very well be a YMMV.

As an aside I occasionally lost some skin when trying to reach an inaccessible tube and getting my arm too close to the picture tube's high voltage wire. Getting zapped was uncomfortable, but worse it caused my arm to involuntarily jerk back and often (with my luck) it connected with a sharp protrusion of the chassis on the way out.

In the middle 60s I worked testing newly manufactured GE mainframes. You would have thought board testing would have caught all board problems but often when a machine had a problem it was caused by a (new) bad board. So board swapping was a still valid troubleshooting method even when testing at the new system level.

[Steve]

The waters are even more treacherous when looking for a tech to hire and train for an employee.

[Scott Lurndal]

Company I co-founded in 2004 built an ASIC (distributed node controller). A very complicated part. When we got the first (untested) samples from the fab, we plugged one into a test board and ... nothing. I would have spent hours trying to figure out why it wasn't working, but the ASIC architect just swapped it for the next one in the tray and it came right up. We never did find a bug in the part that required a re-spin or metal layer change by the fab.

scott

[PaxPerPoten]

Howard Sam's made full schematics and parts list along with layouts of every TV made in those days. In later years you could buy each years sets on Cd or DVD.