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Condenser boiler only working when hot water is

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Hi, hoping for some helpful advice. Sorry detailed story coming up... My gas condenser boiler recently had its annual servicing by a Gas Safe engineer but a week later when the weather turned cold… Read More
Bishbash Avatar
7m, 3w agoPosted 7 months, 3 weeks ago
Hi, hoping for some helpful advice. Sorry detailed story coming up...

My gas condenser boiler recently had its annual servicing by a Gas Safe engineer but a week later when the weather turned colder I noticed the central heating was not coming on. I checked the programming unit and found the heating only came on when the hot water is on. This is unusual as earlier this year when we needed the heating on, it worked without the need of the hot water switched on.

We called the engineer back who was puzzled by the problem and cited that he only checked and cleaned the boiler and didn't touch anything else. He suggested I change the programming unit which I did but the problem is still happening. I called the engineer a 3rd time only to be told he is on a long term job so can't visit again for a couple of weeks.

In the meantime, (luckily) we still get heating but only with hot water. Please can anyone suggest why the problem is occuring?

Many thanks
Bishbash Avatar
7m, 3w agoPosted 7 months, 3 weeks ago
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(23) Jump to unreadPost an answer
Responses/page:
#1
No expert, but when I have heating problems I check if there is enough water pressure in the system. Check those gauges and if the black needle dropped below the red top it up using inlet valve.
#2
Is it a combination or system boiler?

If system boiler sounds like an electrical fault. Likely at the heating motorised valve or less likely at the programmer. When motor moves valve should also make circuit live activating boiler. Sounds possible only hot water valve making circuit.
#3
Is it a combi boiler or a boiler with a hot water tank. Can u give the model number of the boiler as it will help.
#4
developers
Is it a combination or system boiler?
If system boiler sounds like an electrical fault. Likely at the heating motorised valve or less likely at the programmer. When motor moves valve should also make circuit live activating boiler. Sounds possible only hot water valve making circuit.

It's a system condenser boiler and the programmer unit is brand new (installed a week ago). Where is the heating motorised valve located?


Edited By: Bishbash on Dec 01, 2016 21:24
#5
kash2013
Is it a combi boiler or a boiler with a hot water tank. Can u give the model number of the boiler as it will help.

It's a Baxi Dolo boiler with hot water tank.
#6
It will be a faulty motorized valve or room thermostat. The room thermostat when turned up should send power to the brown of the heating valve. Valves are most commonly in the cylinder cupboard but not allways. There may only be one valve for heating and hot water functions, if so find out what wire should be live when room stat is turned up.
#7
tubbs321
It will be a faulty motorized valve or room thermostat. The room thermostat when turned up should send power to the brown of the heating valve. Valves are most commonly in the cylinder cupboard but not allways. There may only be one valve for heating and hot water functions, if so find out what wire should be live when room stat is turned up.
I thought about the thermostat too but if that was not making the circuit the heating wouldn't come on even with the water on as the valve wouldn't open if it's wired right.
#8
Thank you for the answers. Will check out the valve and thermostat.
#9
Diverter valve has stuck in one position.
#10
If DIYCRUISER is not right and you want to rule out the Stat...., And if you are competent and confident enough. The thermostat is just an On/Off switch . You want to make it On all the time to test the system.
Isolate the power to the CH system to ensure no power to the Thermostat.
Take the front cover off the roomstat.
Check there is no power to the unit.
If you have a light switch cover or terminal block in the garage, connect the blue and brown across the terminal block/switch. Restart the CH and see if the system responds (Heats) continuously.
http://thumbsnap.com/s/URAGAvX7.jpg
#11
As above sounds like your 3 way motorised valve . when tank temp below set value (tank thermostat) sends hot water to tank , when room temp below room thermostat sends hot water to rads , if both below temp sends hot water to both .

Mine failed (stuck ) and got away with tapping it with a small hammer for a while to free it . Had to change it eventually - not difficult or expensive - 3 pipe connections and I think 4 wires in a Terminal Block . Of course you need to drain the system down first to below the valve level .
#12
Thank you all so very much. Will try all the suggestions here and report back if successful. Cheers x
#13
Thank you so much for making extra effort to post a photo. Much appreciated. Hoping hubby can work through all this advice this weekend!

getmeone
If DIYCRUISER is not right and you want to rule out the Stat...., And if you are competent and confident enough. The thermostat is just an On/Off switch . You want to make it On all the time to test the system.
Isolate the power to the CH system to ensure no power to the Thermostat.
Take the front cover off the roomstat.
Check there is no power to the unit.
If you have a light switch cover or terminal block in the garage, connect the blue and brown across the terminal block/switch. Restart the CH and see if the system responds (Heats) continuously.
http://thumbsnap.com/s/URAGAvX7.jpg


Edited By: Bishbash on Dec 02, 2016 16:17: spelling
#14
Also, in cold weather the external overflow/extract pipe can freeze up and block up - which caused mine to shut off in cold weather. Used to have to pour hot water on the pipe to get it going again until i insulated and cut a relief section out.


What could be the cause?
In long periods of cold weather, the condensate pipe of your boiler - a waste pipe that carries condensation from the boiler to your drain outside - can freeze, especially if it's exposed or incorrectly installed.
This can leave you without heat and hot water as the boiler has an in-built safety device to prevent any damage to the system.

Edited By: Lefty on Dec 02, 2016 09:12
#15
Lefty
Also, in cold weather the external overflow/extract pipe can freeze up and block up - which caused mine to shut off in cold weather. Used to have to pour hot water on the pipe to get it going again until i insulated and cut a relief section out.
What could be the cause?
In long periods of cold weather, the condensate pipe of your boiler - a waste pipe that carries condensation from the boiler to your drain outside - can freeze, especially if it's exposed or incorrectly installed.
This can leave you without heat and hot water as the boiler has an in-built safety device to prevent any damage to the system.
That is indeed true but would shut down the boiler completely . OP has already stated Hot water is ok (therefore boiler working) but heating only works when hot water on - hence the 3 way valve .
banned#16
Probably port valve motor failure.

http://www.screwfix.com/p/drayton-synchronous-motor/28670#_=p

£16 & an easy fix or you might need to replace the whole port valve depending on how old it is.

Edited By: YouDontWantToKnow on Dec 02, 2016 10:55
#17
Probably need to check to see whether the hot water tank isn't being heated up by the heating element.
#18
"Probably need to check to see whether the hot water tank isn't being heated up by the heating element". Caulcano is right, make sure immersion heater isn't on if you have one. Also it can be the microswitch in the valve that is faulty, or the motor. Not sure if Honeywell and Drayton share the same spare parts ie motors and switches. Most valves have a seperate base and head, so pipework doesn't have to be touched, just fit new head onto original base and connect wires like for like. If the microswitch is faulty it won't switch boiler on when valve opens for heating. The grey wire of the valve is usually permanent live, and this switches to the usually orange wire which then switches the boiler on.
#19
Thank you all again for the helpful replies about my problem of central heating not coming on except when hot water is on. We have tested the room thermostat idea and it's not that so next is looking at the motorised valve. Don't want to touch any gas parts but it's worth an initial look this weekend.

Cheers all :)
#20
Bishbash
Thank you all again for the helpful replies about my problem of central heating not coming on except when hot water is on. We have tested the room thermostat idea and it's not that so next is looking at the motorised valve. Don't want to touch any gas parts but it's worth an initial look this weekend.
Cheers all :)
Its the valve assembly. Microswitch or mechanically seized. Unlikely to be the controller.


Edited By: getmeone on Dec 05, 2016 07:10: Spelling
#21
Would be good to hear if we helped sort it out for you.
#22
Hi. Nothing to report yet as my plumber is coming round next week to have a look :)


developers
Would be good to hear if we helped sort it out for you.
#23
Happy new year HUKD friends!

Just wanted to let the kind posters on here know how my heating problem worked out. To recap, my heating would not come on unless my hot water was also on. My plumber confirmed it was the motorised valve (situated in loft near water tank) and once he replaced it, the system worked as normal.

I didn't get any Rudolph prizes this year but the helpful advice made up for it 8) Thank you all x

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