Central heating advice needed!

[Deanxm]

The pump should not be set on speed 3, it should be on 1, if the system is badly laid out the pump can draw air from the vent on high speeds so watch out for that.

D

[Mandrake]

The pump should not be set on speed 3, it should be on 1, if the system is badly laid out the pump can draw air from the vent on high speeds so watch out for that.

Yes I had read some months ago that having the pump speed too high on a gravity fed system can cause recirculation through the header tank and subsequent air ingress, I dropped it from 3 down to 2 a few months ago. I tried 1 as well but found the flow rate was too low causing radiators to take too long to warm up and causing the boiler to keep cycling off before the system was up to temperature.

Two seems to be a happy medium with the current pump and system. It will be interesting to see what setting works best for the new pump - it has both a fixed speed (1,2,3) mode with similar flow rates to the 1,2,3 settings on the original pump but also a "proportional pressure" mode where it reduces pressure with reduced flow instead of allowing it to increase. Quite how that will interact with the setting of the automatic bypass valve will be interesting.

[Mandrake]

Ok here comes one of my trade mark long posts, so put your propeller caps on and sit back.

The system is back up and running nicely with just one minor issue remaining to sort.

I decided before any new pump went in I would clean and flush the system as well as I could (short of getting someone in to power flush again) given that debris in the system that came loose last time I drained the system could have been the cause of some of the noise, so last Wednesday I put some Sentinel X400 cleaner in via a radiator and let it run in the system for a few days before draining the system and changing the pump...

I had a look inside the new pump to see how the impeller was constructed and attached, and it is indeed some kind of composite material or perhaps special plastic:



It appears to be clamped by a stanless steel spigot of some kind, so I can see how it could potentially slip if badly worn...

On Saturday I fully drained the system, filled it up with just water and bled it again, ran it for a while then drained it again. The water was slightly black the first time but seemed clear the second time. I then removed the pump and found this:



At first I was a bit mystified - was the impeller on the old pump metal with some sort of hard painted surface that is now chipping off ? It feels like a thick layer of old paint when you try to chip it off with a finger nail - it doesn't come off easy but the base housing was full of little chipped off pieces...Or is it magnetite and lime scale deposit ??! I'm still not really sure so I will have to have a go at scraping more of it off with a screw driver.

As well as whatever the black flaking stuff is a number of small hard lumps of what I assume is lumps of limescale deposit fell into my tray out of the pump housing when I removed it - a few pieces were as large as 3-4mm across and felt like grains of sand. Now I know what one of the noises was!! My theory is the previous drain down had loosened some small chunks of lime scale somewhere in the system which had got lodged in the impeller scraping their way around and around inside the housing...

After discovering this I decided I needed to flush the system as much as possible before the final fill, as well as adding limescale remover in the final fill (I used Sentinel X200) as well as inhibitor. (Sentinel X100)

I also found that while it wasn't seized the automatic bypass valve was indeed sticking and not always sealing properly so I made the right call replacing that too. (The old one seems a bit flimsy inside now I've seen inside it, the new one does seem to be better designed)

So I fitted the new pump, new gate valves, automatic bypass valve and filled the system up and bled with water only, ran it for a short time, bled it down and filled it up again, then ran it for a few hours that evening to asses the noise and performance, and check for leaks. The pump is unbelievably quiet - the old one you could always hear running from the kitchen even when it wasn't acting up, but when it decided to throw a wobbly it would actually wake us up in bed upstairs or be heard over the TV in the living room...

This one I can't hear at all from the kitchen, I have to go out into the utility room and open the boiler room door and then I can just barely hear any noise from the pump. Before and after pics:





The old gate valves were well and truly seized - now that I've seen how those screw driver slot types work I would never buy any as they are just asking to seize up with age, and you just can't get the purchase you need with a screwdriver... the tap style gate valve that I fitted are a far better design I think and only slightly dearer.

The next morning I drained the system down again and filled it up again - this time the water was pretty clean but I noticed a little bit of yellow/orange colour to it (rust I guess) it so I had an idea - what if I use the pump as a circulator with the boiler turned off while the drain cock is open ? As long as the drain cock is not open too much the cistern will keep the system topped up and prevent the pump running dry. That way the water comes down from the header cistern, is drawn through the heat exchanger, through all radiators, then out through the drain.

So I did this and to my amazement it worked extremely well - the slight yellow colour that I got when I did a normal drain (including opening all the air valves on the radiators of course) was replaced by a deep yellow/orange colour when flushing through the entire system when described. I ended up leaving it flushing for about 3 hours and it took a good two hours for the water to run completely clear.

I then completely drained it and filled it up again this time with X100 and X200 in place, bled the system and let the pump run with the boiler off for 30 mins to fully mix the additives before turning the boiler back on, and stopped the system to bleed a couple of times.

End result: The pump is completely silent, no more barrel of marbles sound, no more dry bearing squeal, no noise at all really. All the radiators heat up quickly and are running nicely.

The only issue that remains at the moment is the system is still a bit prone to vapour locking if you turn the boiler stat right up, or after the the wall stat (and therefore pump) have been off for half an hour or so. I think there are a few contributing factors to that -

One is that I think there is a bit of lime scale in the heat exchanger causing localised hot spots so there is a tendency to produce some steam when running near the upper temperature limit - if this builds up sufficiently this can trigger a vapour lock situation. I'm hoping that after the X200 has been in for a few weeks this will lessen.

The second is that the mechanical thermostat on the boiler is getting a little bit flakey and while it works "OK" most of the time I think once in a while it does let the boiler go 10 even 15 degrees past it's set temperature, so if you have it set near maximum it exceeds the maximum safe temperature (~80 degrees) thus triggering a runaway vapour lock situation, probably compounded by lime scale hotspots.

I'm still waiting for that external digital temperature controller to arrive - I don't know for sure but I think that a much more accurate and fast responding stat will solve this issue.

The third is the heat soak issue with the pump switching off with the boiler - my plan there is to use a cylinder pipe thermostat clamped to the inlet pipe for the pump wired up as a pump overrun so that when the wall stat goes off the pump will keep running until the flow drops to a certain temperature, just like the pump overrun on a modern boiler...

All in all I'm very happy with the results, with this being my first major work on a system like this, it's certainly given me something mechanical to play with in the blessed absence of any car problems recently!

PS anyone know a good solution to clean off copper sulphate corrosion on soldered pipes ?

[dnsey]

Can you set the hysteresis of the electronic controller? If not, you might find that it switches every few seconds as the temperature varies by a degree or so.
A more sophisticated approach is 'burst fire', which runs the boiler for decreasing periods as the target temperature is approached, and thus minimises overshoot.

[wurlycorner]

PS anyone know a good solution to clean off copper sulphate corrosion on soldered pipes ?

A small brass wire brush will rub that back nicely, without damaging the pipework/solder.

[Mandrake]

Can you set the hysteresis of the electronic controller? If not, you might find that it switches every few seconds as the temperature varies by a degree or so.

Yes, it's a controller designed specifically for controlling heating/cooling systems, the hysteresis is fully programmable between 1 and 15 degrees - I'll probably start with about 8 degrees which I think is typical of a boiler stat. It also has an optional timer delay which sets a minimum time delay between cut-out and cut-in of between 1 and 10 minutes.

For example say the temperature was set to 70 degrees, hysteresis 8 degrees and delay 3 minutes. It would stay on until the boiler reached 70 degrees, then would remain off until the temperature dropped to 62 degrees or below and a minimum of 3 minutes had passed. The time delay could be used to minimise cycling rate even with a smaller hysteresis like 5 degrees. (I wouldn't go less than about 5 degrees though) Between the adjustable time delay and hysteresis I should be able to tune the cycling behaviour to something optimal.

A more sophisticated approach is 'burst fire', which runs the boiler for decreasing periods as the target temperature is approached, and thus minimises overshoot.

That's a clever idea - a bit like TPI for a wall stat... unlike a modern boiler there is no flame modulation which runs the flame at full blast when the flow temperature is low and then backs it off as the cut-out temperature is approached, it just runs full blast until it shuts off.

Combine that with a slow responding mechanical thermostat whose probe is located in the heat exchanger body instead of an electronic immersion sensor in the output pipe flow and a heavy cast iron heat exchanger and you have a recipe for temperature overshoot, especially if the ABV is partially open allowing hot water to loop back around much quicker allowing for a much faster temperature rise in the boiler...

Unfortunately the controller I've picked doesn't support burst fire so I'll see how I get on without it but keep it in mind.

[elma]

Well done Simon, it's been an interesting thread.
I asked a plumber about the copper corrosion once. He told me it is just the modern flux that does it and nothing to worry about, purely cosmetic.

[Mandrake]

Yeah it is just cosmetic, but the appearance does annoy me and it can still be cleaned off...

[RichardW]

Good work Simon! At least you appeared to have fixed it.

We have progressed from walls to roof... it turns out all the nails were rotten, and the wood worm had heavily lunched on the joists and rafters, so it all had to come off. Yesterday we were 'dining al-fresco'. IN the house



I love old houses. NOT!!

[isisalar]

Hi Simon, glad it seems to be all sorted. I just thought I'd point out that you appear to have some amalgam tape above and to the left of your new pump, shown in your latest pictures. This is a very good product for fixing leaks temporarily and could be working, worth checking out though, might be letting in a bit of air which will encourage corrosion.

[Mandrake]

Good work Simon! At least you appeared to have fixed it.

Yep, I'm getting there.

On Monday I noticed two of the TRV valves that were working fine before all the draining and flushing decided they weren't going to co-operate

One didn't seem to want to close - Even turned down to frost protect in a warm room it was still merrily flowing, I had to shut it right down to 0 to get the flow to stop. I thought there might be a bit of flushing debris stuck in the valve so started trying to clear it by turning all other rads off, putting the pump on high, tapping it gently etc, but it turned out to be a failed TRV head! Grr...

I guess the wax pellet inside went "pop" because on comparing it with another spare TRV head of the same make that I had with both turned to 0 the plastic pin was hardly protruding while on the working one it was protruding nearly 10mm further. After noticing that I also noticed there was a small bit of greasy substance on the top of the valve body pin. Swapped the spare head on and that one is working OK.

The living room one was also playing up, but in a different way - that radiator has a motorised TRV on it and I was noticing that it wasn't coming quite up to the set temperature (about 1 degree low) and on manually operating the TRV I noticed that the flow wasn't starting until the motor was wound nearly all the way out. Hmm... so I pulled the head off and found the pin in the valve is "sticky" if I push it in with my finger and gently release it wouldn't come out smoothly but in small jumps. As the motorised TRV releases the pin very slowly I can see that it would tend to stick until it fully unwound.

A few light taps of the pin with a hammer and pushing it in and out with a finger and the pin seems to have freed up and is working fine now - my guess is that one of the chemicals I added, possibly the X400 cleaner has caused the rubber seal in the valve to swell slightly.. Grr again...that was a new valve body in February... seems to be OK now but I will keep an eye on it.

The digital temperature controller arrived yesterday so I've installed it in a temporary fashion. Boy does that thing respond fast - I had a lot of fun testing it with cups of hot and cold water, playing around with its programming, alarm modes etc. (Yes I'm just an overgrown kid... )

The sensor is strapped to the copper heat exchanger output pipe an inch or so away from the heat exchanger and the relay is wired in series with the power feed to the boiler, with the built in boiler stat turned right up as a safety backup.

I have the minimum and maximum temperature range set to 50 and 82 degrees, (the manual for the boiler quotes a maximum temperature of 82 so I'll stick with that) the over temperature alarm set to 8 degrees so it will start beeping if the temperature goes 8 degrees over the set temperature, and hysteresis set to 5 degrees.

And it works brilliantly. When the rads are still heating up there is only about 1 degree of overshoot and when they are fully hot it overshoots about 5 degrees due to thermal mass of the heat exchanger.

I was testing it right up to the maximum 82 degrees set point, where it will overshoot to about 87 degrees after the burner has gone off. I'm not sure if its the faster thermostat or whether the descaler is starting to kick in but I was not able to trigger vapour lock at all.

Even when I closed all the radiators so that all the flow was going through the automatic bypass valve (thus very little to dissipate heat) which would have previously been guaranteed vapour lock within minutes it would switch off at 82 degrees and climb to about 87 degrees before falling back, and despite the odd "gurgle" from the boiler when peaking at 87 degrees it is no longer vapour locking while the pump is running. Radiator temperature are getting right up to 80 degrees in this condition, which is all that could be expected of an old system.

If I turned off the pump and boiler when it was sitting peaked at 87 degrees and turned it back on after 15 minutes I was still able to provoke vapour lock though, not surprising, so I think a pipe stat wired to give temperature controlled pump overrun will solve that issue as well.

We have progressed from walls to roof... it turns out all the nails were rotten, and the wood worm had heavily lunched on the joists and rafters, so it all had to come off. Yesterday we were 'dining al-fresco'. IN the house



I love old houses. NOT!!

You're a braver man than me!! Are you trying to do all the work yourself or do you have some reinforcements ?

[Hell Razor5543]

You know why all this is, don't you. Something has noticed that, since you have no longer got 'The Problem Child' to keep you occupied, you are able (to a degree) to sit back and relax, so they chucked you a whole lot of new stuff to get on with.

[Mandrake]

Somehow missed your post until now Paul...

Hi Simon, glad it seems to be all sorted. I just thought I'd point out that you appear to have some amalgam tape above and to the left of your new pump, shown in your latest pictures. This is a very good product for fixing leaks temporarily and could be working, worth checking out though, might be letting in a bit of air which will encourage corrosion.

I was wondering if anyone would comment on the black tape.

Don't worry, it's not sealing any leaks its wrapped around solid pipe. The reason I put it there ages ago was so that I could use my IR Temperature gun to measure the flow temperature during troubleshooting - bare copper pipe has an extremely low emissivity which also varies greatly depending on whether the surface is clean and shiny or dirty so you can't use an IR gun to measure the temperature of a naked copper pipe and expect to get any meaningful result.

The usual trick is to wrap some matt black tape around the pipe - which has an emissivity of about 0.95 - similar to most other matt surfaces, then you can get an accurate reading. The piece at the top was to measure the temperature of the automatic bypass loop to try to ascertain whether there is flow in the bypass loop or not, (to help work out the correct setting) but it turns out that because that length of pipe is so short and copper is such a good conductor it gets hot quickly anyway even if there is no flow through it...

I kind of wish I hadn't put it on there now - its 3M self amalgamating tape and after being there for a few months its gone hard and sticky and is nearly impossible to remove. When I fitted the new pump and gate valves I had to carefully scrape off about an inch of the stuff as the pipe inserts much further into the new gate valve. Getting that off and getting the surface clean so that it would seal well on the new olive but without scratching the pipe in the process was quite a chore and probably the hardest part of the pump swap job.

Regarding air getting in - after the initial first day bleeding I don't seem to be getting any air into the system any more. I think renewing all the fittings around the pump as well as the pump may have helped - I didn't have any problems with the new fittings sealing, they were perfectly leak free first time (I did take quite a bit of care to clean the ends of the pipes etc) so maybe a tiny bit of air was being drawn in around the old fittings - hard to know...

[RichardW]

You're a braver man than me!! Are you trying to do all the work yourself or do you have some reinforcements ?

No, got people in for the main work - that sort of thing is a bit above my tolerable stress level!!