Bosch combi boiler playing up
Discussion
Over the last couple of weeks my combi boiler has been playing up, and has gradually got worse to the point that my shower this morning was cold 
The symptoms are that the hot water is only coming out luke warm, and if i restrict the taps to only a trickle it only ups the temperature a little. The boiler looks to be running fine (kicks in and the flame looks strong) it just can't heat up the water.
After some reading online I will go home tonight and run the hot tap for 5 minutes and see if the flow and return are heating up on the central heating, I will also check the function of the heating system as i am not sure if it is working or not.
Does anybody have any advice or tips on what to look at? In my mind it could either be the diverter sending the hot water around the CH system (which i will check) or maybe a build up of sludge in the heat exchanger?
How can I flush the system through, is this something I can do myself? I would rather not pay someone to come out (I am skint and a service engineer by trade so am capable of doing the non-gas bits myself but have no experience of domestic systems as this is my first house)
All help appreciated
The symptoms are that the hot water is only coming out luke warm, and if i restrict the taps to only a trickle it only ups the temperature a little. The boiler looks to be running fine (kicks in and the flame looks strong) it just can't heat up the water.
After some reading online I will go home tonight and run the hot tap for 5 minutes and see if the flow and return are heating up on the central heating, I will also check the function of the heating system as i am not sure if it is working or not.
Does anybody have any advice or tips on what to look at? In my mind it could either be the diverter sending the hot water around the CH system (which i will check) or maybe a build up of sludge in the heat exchanger?
How can I flush the system through, is this something I can do myself? I would rather not pay someone to come out (I am skint and a service engineer by trade so am capable of doing the non-gas bits myself but have no experience of domestic systems as this is my first house)
All help appreciated
First check if the central heating is working, combo boilers often have a diverter valve which switches the flow of water to the heat exchanger from CH to DHW, these can fail. If the rads are getting hot when you run HW then this could be the problem.
Is the boiler cutting in and out when you run HW? Or does it stay lit as normal?
Is the boiler cutting in and out when you run HW? Or does it stay lit as normal?
At a guess I'd say it is likely to be a blocked plate heat exchanger or a faulty diverter valve.
Symptoms are similar for both (heat tracing through the heating pipework), but if the boiler is constantly cutting in and out when running the hot tap, I'd lean more towards the PHE being blocked.
Can usually get away with removing the PHE and giving the primary part of the PHE a blasting through back and forth with a hose pipe. You'll see little black clumps flying out.
If it is the diverter valve, some of the rads usually start to warm up when the hot tap is run for a while.
If it turns out to be the PHE, it may be worth investing in a powerflush or a magnetic filter on the heating return to prevent it happening again.
Symptoms are similar for both (heat tracing through the heating pipework), but if the boiler is constantly cutting in and out when running the hot tap, I'd lean more towards the PHE being blocked.
Can usually get away with removing the PHE and giving the primary part of the PHE a blasting through back and forth with a hose pipe. You'll see little black clumps flying out.
If it is the diverter valve, some of the rads usually start to warm up when the hot tap is run for a while.
If it turns out to be the PHE, it may be worth investing in a powerflush or a magnetic filter on the heating return to prevent it happening again.
Hi everyone,
I have just tried running the kitchen tap on hot at only a trickle, and it does eventually get hot. I ran it for around 5 minutes and the central heating flow was just as hot as the domestic hot water and the upstairs radiators were beginning to get warm!
The boiler is a Worcester Bosch 240 Combi RSF
I have just tried running the kitchen tap on hot at only a trickle, and it does eventually get hot. I ran it for around 5 minutes and the central heating flow was just as hot as the domestic hot water and the upstairs radiators were beginning to get warm!
The boiler is a Worcester Bosch 240 Combi RSF
The 240 has a calorifier IIRC, when these block up the boiler usually goes in to overheat. Most likely the diverter valve. If you remove the front panel and lower the control panel, you see a brass valve with a black switch on the bottom left of the boiler, that is the diverter valve.
They are fairly easy to change if you have good access to either side of the boiler. Some tips though, the isolation valves for the flow and return will probably leak once used, there is a drain off on the side of the calorifier to drain the boiler fully and place a towel under the valve when removing it, there is always some left over water that likes to run into the PCB housing!
They are fairly easy to change if you have good access to either side of the boiler. Some tips though, the isolation valves for the flow and return will probably leak once used, there is a drain off on the side of the calorifier to drain the boiler fully and place a towel under the valve when removing it, there is always some left over water that likes to run into the PCB housing!
Jobless said:
The 240 has a calorifier IIRC, when these block up the boiler usually goes in to overheat. Most likely the diverter valve. If you remove the front panel and lower the control panel, you see a brass valve with a black switch on the bottom left of the boiler, that is the diverter valve.
They are fairly easy to change if you have good access to either side of the boiler. Some tips though, the isolation valves for the flow and return will probably leak once used, there is a drain off on the side of the calorifier to drain the boiler fully and place a towel under the valve when removing it, there is always some left over water that likes to run into the PCB housing!
Yep around £69 + vat did one last week on bf version, comes with new washer kit and o ring for sliding sleeve connection to calorifier, isolation valves will leak as said so drain down and change them too, fairly easyThey are fairly easy to change if you have good access to either side of the boiler. Some tips though, the isolation valves for the flow and return will probably leak once used, there is a drain off on the side of the calorifier to drain the boiler fully and place a towel under the valve when removing it, there is always some left over water that likes to run into the PCB housing!
After 20 minutes looking online and finding the part number in my servicing instruction booklet this is the cheapest I have found 
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
AceOfHearts said:
After 20 minutes looking online and finding the part number in my servicing instruction booklet this is the cheapest I have found
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
Bang on pal, that will sort it, manual will also give you the steps to fit it etchttp://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&am...
AceOfHearts said:
The manual says basically remove and replace so should be quite self explanatory 
I will get all new valves as well, nothing worse than trying to do a job when all the valves are letting by
Another tip I forgot, when draining the boiler, remove the microswitch on the diverter valve and pull the small spindle towards you using a set of pliers, this will aid in draining the main heat exchanger!I will get all new valves as well, nothing worse than trying to do a job when all the valves are letting by
Dr. Rick, you have a new-ish Vaillant IIRC? Depending on the model, the diverters on those are one of the easiest to change, they have a stepper motor instead of a pressure differential assembly, so fewer wet connections.
You do realise you can turn the preheat off if it causing you issues? Just turn the DHW all the way down for a few moments, then back to the desired temp. Turn it back to maximum to re-activate.
Apologies if I have you confused with someone else!
Jobless said:
Dr. Rick, you have a new-ish Vaillant IIRC? Depending on the model, the diverters on those are one of the easiest to change, they have a stepper motor instead of a pressure differential assembly, so fewer wet connections.
You do realise you can turn the preheat off if it causing you issues? Just turn the DHW all the way down for a few moments, then back to the desired temp. Turn it back to maximum to re-activate.
Apologies if I have you confused with someone else!
We had a Vaillant gas boiler in the house before last (moved 3 times in 3 yrs, don't ask).You do realise you can turn the preheat off if it causing you issues? Just turn the DHW all the way down for a few moments, then back to the desired temp. Turn it back to maximum to re-activate.
Apologies if I have you confused with someone else!
The pre-heat is an odd one. The oile fired Rhino boiler we have doesn't appear to fire if the daisy wheel timer is set to be 'off'. I haven't sat there for minutes on end to see if eventually the hot water makes it through, but given the utility sink is next to the boiler, I didn't expect much delay and the boiler never fired.
When the time block is 'on' the pre-heat fires for a few minutes and then you can get hot water with the boiler topping up the pre-heat vessel I assume. There's nothing in the destructions to separate the timer from teh pre-heat as far as I can tell.
We have a plumber on site at the minute for replacing the timer set-up (to introduce a wall-stat) and I've asked him to look at the pre-heat and the DHW heat-bleed (diverter valve) at the same time.
Dr Rick
Thought I would update this thread, basically the boiler seemed to sort itself and hands been running OK for almost a year, but last week went back to the same old tricks.
I have just (today) replaced the diverter valve and have repressurised the central heating. Everything kicks on when the hot water is turned on and there is still no hot water!
I am thinking now that it might be the water-water heat exchanger as I can feel it getting hot, and can feel the cold mains coming in but no hot coming out. Very frustrating
I have just (today) replaced the diverter valve and have repressurised the central heating. Everything kicks on when the hot water is turned on and there is still no hot water!
I am thinking now that it might be the water-water heat exchanger as I can feel it getting hot, and can feel the cold mains coming in but no hot coming out. Very frustrating
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