Coal Fired CH Issue - advice requested

GlynD

We moved into this bungalow three years ago. It has a dual system oil/coal with a Baxi Burnall fire fitted.

I was personally disappointed by the heat output to the rads from the fire but my only yardsticks were previous ownership of homes which had conventional open fires or Safona glass fronted. The output wouldn't have been enough to do more than take the chill off the rads however until last night.

We lit the fire and let it burn for around 60 minutes before switching the pump on. When we did there was a loud banging for around three seconds which startled us and scared the cat - the pump is in a wooden cupboard next to the fireplace and that undoubtedly amplified the noise. Obviously we switched the pump off immediately.

We waited a minute and then switched the pump on again. No banging this time just a bit of gurgling from the back boiler. When I went to check the rads they were piping hot, even beyond what our oil boiler normally achieves on the low setting we use.

My first feeling was that a motorised valve had been stuck for some time and had freed itself off but checking in the cupboard I can see no valve, just the pump. Is it possible this pump was faulty or blocked and what we heard was it freeing itself off?

A factor which may be important is the fact that the couple who were here before us were in their 80's and may have used the oil system for convenience. We know we had to fit a whirly chimney cowl to stop downdraughted smoke coming into the room and don't believe anyone would have lived here and put up with that.

What would a tradesman's recommendation be at the moment? Do we need a new pump? How much would it cost to have one fitted?

wrightk

i am by no means an expert, but i do run a stove myself which does the hot water and heating system. i would have thought that the pump would have some sort of stat on it to automatically turn the pump on for you. what would happen if you didnt go and turn the pump on?! or if you forgot?
is it not possible that you left it too long before turning the pump on causing the almost boiling water to rush through the pipes with force that clattered the pipes and when you turned it back on a minute later it was fine because the water had previously had a chance to circulate through the system?

GlynD

We don't have a stat but we do have a head loss rad.

I accept what you say about letting the water get too hot and the possible consequences but that wouldn't explain the fact that the radiator output has changed so dramatically.

wrightk

another explanation is that you may have had a fairly large airlock in the system near the pump. we had our system completely repiped last year due to it being incorrectly installed and no radiators upstairs working. after it was repiped there was a large airlock in the system which took the plumber about an hour to shift and it was very close to the pump. The rads upstairs were working but not as warm as they should have been until this was sorted. this may be the cause. its also worth noting that any 'bang' in the pipes like you have suggested will be amplified by the cupboard that the boiler is in and the whole pipework in the system resonating, so the bang probably sounded a lot worse than it was.
if the rads were working previously just cooler the pump isnt the issue because you are getting flow. simple way to check is to hold your hand over the pump you will feel it vibrating slightly.make sure your pump is set on the lowest speed possible

comeandgo

Many years ago we had a the same system as you and we had to let the fire burn for about an hour before we put the radiators on otherwise the water never really got hot enough to get the radiators up to any heat.

malc_b

I used to have CH run from a coal room heater. This has 2 sets of pipework. Right side was gravity feed (hot water rises of course, cold sinks). This had no pump. It fed the HW cylinder and a bathroom radiator. This was a heat dump to absorb the heat from the fire running at bare minimum. The fire had it's own thermostat that operated an air valve. The left was a pumped system that fed all the radiators. When the pump turned on the water in the fire jacket cooled and the fire thermostat opened the air valve making the fire burn harder.

It sounds like you pump had stuck and then freed itself. Another possibility is that you have a non-return valve in the pump line that stuck then opened. My system used to have this. It wasn't used as a non-return but just as spring loaded valve so that the pumped side would not gravity feed like the right. I light spring closed valve is enough to stop gravity feed but makes no difference when the pump runs.

GlynD

wrightk wrote: »

another explanation is that you may have had a fairly large airlock in the system near the pump. we had our system completely repiped last year due to it being incorrectly installed and no radiators upstairs working. after it was repiped there was a large airlock in the system which took the plumber about an hour to shift and it was very close to the pump. The rads upstairs were working but not as warm as they should have been until this was sorted. this may be the cause. its also worth noting that any 'bang' in the pipes like you have suggested will be amplified by the cupboard that the boiler is in and the whole pipework in the system resonating, so the bang probably sounded a lot worse than it was.
if the rads were working previously just cooler the pump isnt the issue because you are getting flow. simple way to check is to hold your hand over the pump you will feel it vibrating slightly.make sure your pump is set on the lowest speed possible

I like your thinking. If it was an airlock though it's been there for at least 3 1/2 years. Having worked with CH systems before I did feel the pump for vibration and even took the inspection cap off to ensure the spindle was turning. We've since had out boiler serviced and asked the engineer to give his opinion. It's a very good quality pump apparently (although that doesn't make it immune from faults). He's of a like opinion to me, just keep an eye on it and see how it works over a period of time.

malc_b wrote: »

I used to have CH run from a coal room heater. This has 2 sets of pipework. Right side was gravity feed (hot water rises of course, cold sinks). This had no pump. It fed the HW cylinder and a bathroom radiator. This was a heat dump to absorb the heat from the fire running at bare minimum. The fire had it's own thermostat that operated an air valve. The left was a pumped system that fed all the radiators. When the pump turned on the water in the fire jacket cooled and the fire thermostat opened the air valve making the fire burn harder.

It sounds like you pump had stuck and then freed itself. Another possibility is that you have a non-return valve in the pump line that stuck then opened. My system used to have this. It wasn't used as a non-return but just as spring loaded valve so that the pumped side would not gravity feed like the right. I light spring closed valve is enough to stop gravity feed but makes no difference when the pump runs.

Quite possible the pump was running under par and then freed itself. There is no non-return valve at the pump location, it's fitted beside the hot tank. I did think of that but have now discounted the theory.

I suppose I should just be thankful that the system has cured itself of whatever had been ailing it and we now have fantastic output from the fire. I think that'll mean a considerable reduction in the use of oil for this coming winter.