UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > General Vintage Technology Discussions

Notices

General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc.

Closed Thread
 
Thread Tools
Old 1st Jan 2016, 6:30 pm   #21
Audio1950
Dekatron
 
Join Date: Nov 2008
Location: Whittlesey, near Peterborough, Cambridgeshire, UK.
Posts: 3,758
Default Re: Room Thermostat problem

Quote:
Originally Posted by Lucien Nunes View Post
So the boiler has no electronics and the pump is fed separately from the same switched live. What motorised valve(s) do you have?
These are the two Honeywell motorised valves.
Attached Thumbnails
Click image for larger version

Name:	P1040062.JPG
Views:	173
Size:	112.7 KB
ID:	117643  
Audio1950 is offline  
Old 1st Jan 2016, 7:23 pm   #22
ctc15
Pentode
 
Join Date: Oct 2005
Location: Barnet, London, UK.
Posts: 167
Default Re: Room Thermostat problem

Hi I have used a R-C contact suppressor across the contacts to stop this problem. This is a 0.1uF capacitor and a 100 ohm resistor connected in series.
This will suppress the arcing and reduce RFI. You can get them from R.S and Maplin etc.
I hope this helps.
Keith
ctc15 is offline  
Old 1st Jan 2016, 7:28 pm   #23
turretslug
Dekatron
 
turretslug's Avatar
 
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
Default Re: Room Thermostat problem

I had just this problem with room thermostat and Honeywell V4073 mid-position valve (bearing in mind Lucien's comments)- a brief, coarse rasping on radios as the room 'stat closed, sometimes accompanied by a quick chatter of gas solenoid (very straightforward old naturally-aspirated balanced flue boiler, NO electronics, just solenoid, cut-outs and pump!)- this was traced to one of the microswitches in the motorised valve going poor contact. The actuator head is straightforwardly removed for working on, with a little more dexterity, the microswitch cover could be finger-nailed off and the contacts cleaned with fine glass-paper. Reassemble, and be contented for around 18 months..... and repeat. I got fed up in the end and replaced the 3A rated PCB microswitches with a different make 5A type. Problem gone for good.

Of course, I ought to mention the non-manufacturer parts disclaimer bit.
turretslug is offline  
Old 1st Jan 2016, 11:50 pm   #24
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: Room Thermostat problem

You seem to have two 2-port valves, probably normal V4043 spring return type. If this is the case, and they are wired and plumbed in the normal S-plan configuration, and one of them is the valve for the heating zone controlled by the room stat, then the stat should only be controlling the ~6W valve motor. In this case it is difficult to see why the stat contacts would be failing unless there is a mistake in the wiring. It might be necessary to start tracing and measuring.

E2A The significance of this bit now suggests a line of enquiry:
Quote:
The last one got to the stage where it actually blew the fuse in the mains switch.
I can't see that any fuse would blow through the winding of the valve motor, no matter how much the stat arcs, as it's little more than a clock motor with wire much finer than the fuse. Either the stat IS switching something else (i.e. it's not true S-plan, by accident or design) or the stat is flashing over to neutral or earth internally. Bimetal room stats are normally equipped with an accelerator heater to reduce overshoot, which requires a neutral. Is the stat itself miswired so that L & N are on N/C and N/O contacts and CFH on common, so that although the system works there is a nasty flashover opportunity while the contacts change state?

Last edited by Lucien Nunes; 2nd Jan 2016 at 12:08 am.
Lucien Nunes is offline  
Old 4th Jan 2016, 11:36 am   #25
Audio1950
Dekatron
 
Join Date: Nov 2008
Location: Whittlesey, near Peterborough, Cambridgeshire, UK.
Posts: 3,758
Default Re: Room Thermostat problem

Thanks to all who have replied. As many posts seem to think it's a wiring fault, I've got a central heating engineer coming tomorrow. Will post results.

Barry
Audio1950 is offline  
Old 5th Jan 2016, 4:13 pm   #26
Audio1950
Dekatron
 
Join Date: Nov 2008
Location: Whittlesey, near Peterborough, Cambridgeshire, UK.
Posts: 3,758
Default Re: Room Thermostat problem

Well, the engineer has checked all the wiring in the thermostat and programmer, and says everything is wired correctly. I may have posted the wrong information, however, in that the thermostat arcs when it's switching the boiler off, not on. Sorry if that makes a difference.
He has now fitted another thermostat, and reckons all will be fine. I remain sceptical, but time will tell.
Thanks to all who contributed advice and help.
Audio1950 is offline  
Old 6th Jan 2016, 12:04 am   #27
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
Default Re: Room Thermostat problem

Arcing when contacts open is typical if the load is inductive. Just what the CR mentioned above is good for suppressing.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 6th Jan 2016, 12:21 am   #28
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: Room Thermostat problem

As far as we can tell, the stat is only switching the valve motor, basically a large clock motor of around 6W. I have had clock motors run successfuly on the few mA passing through a conventional 0.1uF/120R suppressor, e.g. where a contact was supposed to stop a timer when open but the motor carried on running. If you fit an RC, I'd check that the valve runs back smartly and doesn't tend to stick open, and/or choose a small value of C.
Lucien Nunes is offline  
Old 6th Jan 2016, 1:00 am   #29
Phil G4SPZ
Dekatron
 
Phil G4SPZ's Avatar
 
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,736
Default Re: Room Thermostat problem

My previous electro-mechanical 'stat used to arc just before the contacts opened. I cleaned the contacts every couple of years. By rights, good quality bi-metallic thermostats should have a magnet acting against the closing force of the bi-metal element, thus ensuring a quick clean 'snap' action in both directions. I have a modern electronic (wireless) control system now, which brings its own problems (but not arcing contacts!)

Let's hope your new thermostat does the trick long term. As Jim says, if you have an Avometer with an AC current range it would be very enlightening to measure the current actually flowing when the contacts are closed.
__________________
Phil

Optimist [n]: One who is not in possession of the full facts
Phil G4SPZ is offline  
Old 14th Jan 2016, 10:11 pm   #30
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Re: Room Thermostat problem

Suppressing a light load by fitting the RC across the contact certainly can cause malfunctions due to leakage. It's valid to put the RC across the load instead with such things. The RC will still do its job (i.e. reduce DV/DT).

The perils of overcomplicated thermostats are illustrated here (BBC website link)

http://www.bbc.co.uk/news/technology-35311447
__________________
Kevin
McMurdo is offline  
Old 15th Jan 2016, 7:47 am   #31
Hunts smoothing bomb
Octode
 
Hunts smoothing bomb's Avatar
 
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
Default Re: Room Thermostat problem

Room thermostats these days have very small clearance gaps when the contacts are open as they are designed to carry a few mA simply to control the boilers logic.

back in the day they had massive clearance gaps, were designed to carry more current and built more robustly, this problem never arose.

I'm still willing to bet that the CH room stat is wired in a manner that it is carrying the current for the boiler and pump, (it's a no brainer that the load is very inductive because of the arcing that takes place when the contacts break) I know that the system has been verified by a heating engineer but I have seen plentiful wiring errors made by such people, in my experience the electrical side of the system mystifies some of these engineers and they often prefer to use a regular electrician to "wire up" once the plumbing is installed.

We had a case recently at work where we had a brand new system installed to a property and the engineers made such a mess of the electrical system that it did not work from the start! We paid them a discounted fee, sent them on their way and my team rewired the system correctly.

Just my two penneth worth!

Cheers
__________________
Lee
Hunts smoothing bomb is offline  
Old 15th Jan 2016, 1:00 pm   #32
emeritus
Dekatron
 
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
Default Re: Room Thermostat problem

A 240V-rated relay might solve the problem, if you have somewhere to mount it safely. Only "might" mind you: I use three octal-base relays to control my shed light remotely via pushbutton switches to switch two 12V relays that control the load-carrying 240V relay. Although the load is only 160W resistive, (two GLS lamps, one 100W and one 60W), and the contacts are rated 10A, I had to replace the 240V relay last year due to the contacts failing.
emeritus is offline  
Old 15th Jan 2016, 9:37 pm   #33
stevehertz
Dekatron
 
stevehertz's Avatar
 
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
Default Re: Room Thermostat problem

My thermostat 'buzzes' softly for a few seconds when the set (temperature) point is about to change one way or the other. But in over twenty years it's never failed. I suspect that 'whatever is being switched' by the thermostat is electrically too hefty for the rating of the switch over contacts in the stat - hence they only last a year. Find out what is actually being switched by those contacts and check specs to see if they are compatible. Looks like they aren't.
__________________
A digital radio is the latest thing, but a vintage wireless is forever..
stevehertz is offline  
Old 15th Jan 2016, 9:49 pm   #34
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
Default Re: Room Thermostat problem

Personally, I'd see fitting relays to 'fix' what is obviously a mis-wiring-related overload problem to be a horrible bodge.

Get a properly-qualified [not just a '"gas safe' box-ticker-assessed tradesman] HVAC technician to investigate!!

As a first step, you could stick a meter on the wiring to the thermostat and see what current it's handling. Anything more than a few milliamps means you're switching more than the expected "call-for-heat" signal.
G6Tanuki is offline  
Old 15th Jan 2016, 10:13 pm   #35
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Room Thermostat problem

Just a quick note to say fiddling around inside gas boilers is a criminal offence, so I was told. Gas is way off topic, but if it's an electrical problem (sort of on topic) inside a gas boiler unit it still could be an offence to go poking around, property insurance etc instantly void.
Just had a gas safe registered engineer to another property to do a landlords certificate for me, that's what he said.

Stay safe.

Lawrence.
ms660 is offline  
Old 15th Jan 2016, 10:25 pm   #36
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: Room Thermostat problem

I think we're going round in pumped circulation without the current measurement. The system appears to be S-plan and if so, the stat should only be switching the valve motor. If it also switched the supply to the valve microswitch that feeds the boiler and pump (there's no electronics in this boiler, we've established, so their full load should be switched by the valve), then you would get a latch-up condition when both heating and water are on. The HW valve microswitch would backfeed the CH valve motor through the CH microswitch and the heating would stick on until the water went off. Barry doesn't report any actual system misoperation so pending current measurement the indication is that the stat is failing just by switching the 6w motor in the Honeywell valve.
Lucien Nunes is offline  
Old 15th Jan 2016, 10:34 pm   #37
vidjoman
Dekatron
 
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
Default Re: Room Thermostat problem

In my previous house the original thermostat was quite large and the switch was an over centre snap switch that did switch the pump and boiler. It was an old boiler (1980 ish) with no electronic parts, just a setable timer with mechanical switches. We changed the stat to a more modern design and that arced as it switched off. I fitted a relay and that cured the problem. When we changed to boiler to one with electronic controls the stat worked well without arcing and no extra relay as it now only switched a control voltage.
vidjoman is offline  
Old 15th Jan 2016, 11:10 pm   #38
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Re: Room Thermostat problem

My room stat controls the water pump directly, its been in since 1978. Your average modern 240V room stat available for £20 or so will be rated anywhere between 8-16A and is designed for that job. If your stat of choice only has logic-rated contacts...its the wrong choice!
Gas talk is OT for the forum, but electrics wise your connections will only be under a decorative cover which is perfectly acceptable to remove as a user.
__________________
Kevin
McMurdo is offline  
Old 16th Jan 2016, 1:59 am   #39
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: Room Thermostat problem

Quote:
Originally Posted by pwdrive View Post
Gas is way off topic, but if it's an electrical problem (sort of on topic) inside a gas boiler unit it still could be an offence to go poking around, property insurance etc instantly void.
Anything inside a gas boiler, or indeed any gas appliance, IS off topic for this Forum. An external thermostat, however, could be deemed to be part of domestic wiring, as illustrated in the installation instructions left with the user. What you are comfortable with personally is just that, and best not broadcast, just in case!
AC/HL is offline  
Old 16th Jan 2016, 10:42 am   #40
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Room Thermostat problem

Yes, what I should have said is an electrical device associated with a system, The rest is self explanatory, apologies for any confusion.

Lawrence.
ms660 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:14 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.