Difference between revisions of "Central Heating Repair"
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(→Fault-finding: expanded No CH or DHW section) |
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; All systems | ; All systems | ||
: | : | ||
+ | * '''Is boiler firing?''' On older boilers flames can be seen through a window in the combustion chamber: some have a permanent small blue pilot light when the boiler is idling, and all have a mass of flames (often flecked orange/yellow) when the main burner is alight. On newer boilers often there is only an indicator light which, depending on the model of boiler, may not accurately indicate that the boiler is actually running. Whirring and clicking noises from within the boiler usually indicate that the boiler is attempting to light, but not necessarily that it has succeeded in doing so.<br><br>Check the pipes connected to the boiler: at least one should be getting very hot (too hot to hold, only to touch for a second or two) when the boiler is alight. The flue should also be emitting hot gas. '''WARNING!''' flue gases on conventional boilers are hot enough to burn! Even if the flue is not physically accessible (e.g. high up) it should be possible to see a heat haze when the boiler is alight. Condensing boilers (which can usually be identified by having a 22mm plastic pipe connected to them as well as 3, 4 or 6 copper ones) have flues which emit mist when running (although under some conditions the mist may be barely visible). | ||
+ | |||
+ | ==== Boiler not firing ==== | ||
+ | |||
+ | * lockout? / other fault? - boiler fault-finding guide (Ed?) | ||
* power to system? check FCU fuse | * power to system? check FCU fuse | ||
− | * | + | * controls fault? - programmer, thermostats etc |
− | + | ||
− | |||
; Sealed system | ; Sealed system | ||
− | : pressure | + | : pressure low? (much below 1 bar on pressure gauge) |
+ | |||
+ | ==== Boiler firing but no CH or DHW ==== | ||
+ | * pump not running? | ||
=== No CH, DHW OK === | === No CH, DHW OK === | ||
Line 24: | Line 31: | ||
* programmer? | * programmer? | ||
* room stat? | * room stat? | ||
− | * zone valve? | + | * [[Motorised Valves|zone valve]]? |
; Combi boiler | ; Combi boiler | ||
: | : | ||
Line 36: | Line 43: | ||
* programmer? | * programmer? | ||
* cylinder stat? | * cylinder stat? | ||
− | * zone valve? | + | * [[Motorised Valves|zone valve]]? |
; Combi boiler with PHE & diverter valve | ; Combi boiler with PHE & diverter valve | ||
: diverter valve? | : diverter valve? | ||
Line 67: | Line 74: | ||
* timer? | * timer? | ||
* room stat? | * room stat? | ||
− | * zone valve? | + | * [[Motorised Valves|zone valve]]? |
; Some rads on | ; Some rads on |
Revision as of 13:16, 19 March 2007
The article is about diagnosing and fixing faulty Central Heating systems. (This is about systems using hot water as a heat-carrying medium: warm-air systems are sometimes found in the UK but they are not covered here.)
There are separate articles about:
- Central Heating Design which will help you understand what sort of system you have
- Central Heating Operation for help operating a working CH system.
- Boilers describes the main types of boiler.
This article is a skeleton: the main points to be covered are listed but some or all still need to be expanded
Fault-finding
No CH or DHW
- All systems
- Is boiler firing? On older boilers flames can be seen through a window in the combustion chamber: some have a permanent small blue pilot light when the boiler is idling, and all have a mass of flames (often flecked orange/yellow) when the main burner is alight. On newer boilers often there is only an indicator light which, depending on the model of boiler, may not accurately indicate that the boiler is actually running. Whirring and clicking noises from within the boiler usually indicate that the boiler is attempting to light, but not necessarily that it has succeeded in doing so.
Check the pipes connected to the boiler: at least one should be getting very hot (too hot to hold, only to touch for a second or two) when the boiler is alight. The flue should also be emitting hot gas. WARNING! flue gases on conventional boilers are hot enough to burn! Even if the flue is not physically accessible (e.g. high up) it should be possible to see a heat haze when the boiler is alight. Condensing boilers (which can usually be identified by having a 22mm plastic pipe connected to them as well as 3, 4 or 6 copper ones) have flues which emit mist when running (although under some conditions the mist may be barely visible).
Boiler not firing
- lockout? / other fault? - boiler fault-finding guide (Ed?)
- power to system? check FCU fuse
- controls fault? - programmer, thermostats etc
- Sealed system
- pressure low? (much below 1 bar on pressure gauge)
Boiler firing but no CH or DHW
- pump not running?
No CH, DHW OK
- Conventional system
- Is DHW being heated electrically by an immersion heater? In that case treat as for No CH or DHW
- programmer?
- room stat?
- zone valve?
- Combi boiler
- programmer?
- room stat?
- boiler - diverter stucK?
CH OK, no DHW
- Conventional system
- programmer?
- cylinder stat?
- zone valve?
- Combi boiler with PHE & diverter valve
- diverter valve?
- Combi boiler with combined heat exchanger
- flow switch or scaling?
DHW OK, some parts of CH not working
- some rad(s) compeletely cold
- balancing - try turning off other rads
- stuck TRV - take head off pull up pin (carefully - can pull out and leak on some)
- completely full of air - bleed & find cause
- only upstairs working? pump failed?
- only downstairs working? vented system? loss of water?
- some rad(s) lukewarm
- balancing
- faulty TRV
- rad(s) cold at top
- bleeding
- rad(s) cold at bottom
- sludge
CH on when should be off
- All rads on
- timer?
- room stat?
- zone valve?
- Some rads on
- reverse circulation
- rad on DHW circuit - often in bathroom: may be design "feature"
rads constantly need bleeding
- air or hydrogen in system? (lighter test - with care!)
- corrosion:
- inhibitor?
- vented system? - pumping over? - check feed & expansion connections (<150mm apart), header tank level, vent pipe rise & termination height, pump speed setting (old system pump replaced with newer model?)
- air
- pinhole leaks?
- vented system? - pumping over?
- corrosion:
system pressure dropping
This applies to sealed systems only.
Possible causes (see also Ed's Sealed System FAQ)
- leaking Pressure Relief Discharge (PRD) Valve
- problem with expansion vessel:
- lack of air/gas pressure in vessel
- ruptured diaphragm
- leak in pipework
See discussion on uk.d-i-y on Tracing tiny leaks in sealed system
noises
- screeching from pump: vented? loss of water? float valve stuck or feed pipe blocked - sludge or scale
- kettling from boiler: scale - X200 etc
- clicking, knocking from floors & walls: pipework expanding & contracting - expose and free up
- rushing noises from pipes and radiators - air in system?