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croft36

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Our old cast iron central heating boiler isn’t getting the water hot enough anymore! Can’t fathom out why! It runs continuously but the hot water outlet pipes to the radiators and the gravity fed storage tank only get moderately hot, they would usually get too hot to handle. As a consequence shower water not hot enough, radiators not effective. Any suggestions please?
 

D_W

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do you know for sure that it's burning the same amount of gas or oil (whatever it normally would) when it's on? If it's oil, is there a chance that an injector is clogged?
 

porker

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We had similar issues recently with our oil fired system which was a faulty 2 port valve. It only affected the heating but we have an S plan system which has 2 X 2 port valves. If yours is a Y plan system with a single 3 way valve it possibly could be that. Normally there is a lever on the valve to manually overide the motor. Worth checking that to see if it helps. Our symptom was the boiler continuously cycling and very little heat. New motor head fitted (didn't need to touch the plumbing at all) and it was fixed.
 

mikej460

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It sounds like you have a open vented system? If so you might have a problem with the header tank so pressure may have dropped. It could also be caused by a build up of rust scale in the boiler and/or pipes but check for water leaks under the boiler combustion chamber as the heat exchanger could have gone. How old is it?
 

Jos7000

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Older boilers have very little in the way of electronics, however, they do usually have two internal thermostats a high and a low. Perhaps one of those is in need of replacing.
If so, you'll have to hunt online for them as older boiler spares are rarely found in part shops. My boiler is 30+ years old and I am solely responsible for sourcing parts as my gas engineer struggles with his suppliers. But it's not impossible, my only worry is when the heat exchanger gives up.
 

croft36

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Many thanks for all your replies. It is a 1960’s gas boiler, all the jets are clean and working and the flames have their usual appearance. The heat exchanger fins etc have been recently cleaned. The boiler thermostat is working but I have to turn it quite low before it switches burner off, at this point I can hear the pump running. I have now opened the boiler drain and after initial splurge of black and spurting across our breakfast room carpet (fortunately managed to clean carpet with soap and water before her indoors saw it!) the water appears clean but does actually have a few black particles in it. Basically I see it as a kettle full of water, switched on, but not heating the water as it should!. There are no electric valves in the system. I am now going to run it with pump not running ie gravity feed to hot water storage tank, towel rail in bathroom and one radiator only and see if boiler gets up to temperature?
 

Jos7000

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As in moving water, maybe the impellor fins have disintegrated
 

croft36

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Have you checked the water pump is working?
My thinking is that if pump wasn’t working the then stationary water in the boiler would get hotter. Also some radiators would not heat up at all. All our radiators are getting heat, just not enough. I just can’t weigh it up!
 

Glitch

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Doesn't make sense.
If it's on constantly then there is a lot of heat being generated.
If the pump is failing then you'd see the boiler going on and off frequently as the boiler stat kicks in.
Outflow from boiler should be very hot unless the heat exchanger is clogged or scaled.
But if it's constantly fired up any water in the exchanger would be boiling.
Pump might sound like it's running but is it actually moving the water like it should. As Jos said the impellers might have failed.
But poor flow would mean boiler stat kicks in frequently...........

Sounds like you need a heating engineer :)
 

porker

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Agree, if it were cycling constantly then that would make sense and would indicate poor flow but if running all the time then the heat would have to be going somewhere as it would boil the water as previously mentioned. If that were the case I would suspect the pump or scale and/or sludge. Is the pump external and does the pipe feel hot on the feed side? It should do and if not would show there is not enough flow. I've seen broken impellers on pumps so hearing it running does not necessarily mean it is pumping.
 

croft36

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It sounds like you have a open vented system? If so you might have a problem with the header tank so pressure may have dropped. It could also be caused by a build up of rust scale in the boiler and/or pipes but check for water leaks under the boiler combustion chamber as the heat exchanger could have gone. How old is it?
No sign of water leaks.
 

nolly47

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Hi
if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?
 

croft36

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Hi
if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?
There is a hot water cylinder thermostat and room stat in the hall. Most of radiators have thermostatic valves.
 

Jos7000

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Hi
if the boiler has been in since the sixty's you most have had your moneys worth out of it. If there is no m/v valves what controls the temperature in the house? room stat switching the pump on and off?, what controls the hot water the boiler stat?
I'm not sure having the moneysworth out of an older boiler is relevant, it's more of a problem with modern tat that often becomes obsolete the second the warranty is up. Older boilers aren't plagued with the many issues their modern counterparts suffer from and if you factor in the cost of replacement parts and the engineer required to fit them, older boilers are no less economical to own.
 

HOJ

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I would check the pump, been to loads of jobs where the impellers are clogged up with crud, so its pretty much just a spinning disc, still moving water, but without any force.
 

Glitch

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I'm not sure having the moneysworth out of an older boiler is relevant, it's more of a problem with modern tat that often becomes obsolete the second the warranty is up. Older boilers aren't plagued with the many issues their modern counterparts suffer from and if you factor in the cost of replacement parts and the engineer required to fit them, older boilers are no less economical to own.
You have to consider running costs too. A modern condensing boiler is far more efficient between 14%-34% compared to a 30 year old one.
If your old boiler comes with high gas bills you might justify a swap. Plus you might get a grant towards a new one.

No question that modern ones are flimsy though.
 

Rorschach

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You have to consider running costs too. A modern condensing boiler is far more efficient between 14%-34% compared to a 30 year old one.
If your old boiler comes with high gas bills you might justify a swap. Plus you might get a grant towards a new one.

No question that modern ones are flimsy though.
Woah your numbers are way off there. A modern condensing boiler can be over 90% efficient, some almost 99%.

An old boiler from the 60's would have been lucky to be 50% efficient when new, dread to think how bad it is now.
 
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