Black gunge and underperforming pump

[DP]

X800 is a great chemical to clear out the system. BUT, post cleaning, system needs thorough multiple flushed to remove most of the chemicals else pump bearings can succumb to debris and seize. Have seen this happen and have Grunfos pumps with seized bearings

 

[Madrab]

the impellor is likely to be blocked with debris from the rest of the system.

strip the pump out as that may have become clogged up after the clean

 

[DP]

Rab, your and Elkato info solid gold. Pump impeller needs inspecting regardless

 

[Madrab]

Cheers for that @DP, was just a nudge to the OP that isn't wasn't just one person that suggested it but hey ho

 

[mjburrows]

"strip out the pump" isn't that helpful unless you say what to do with it once it's stripped out. And all the evidence I have suggests the impeller was jammed with crap before the clean.

 

[mjburrows]

I think you need to stop worrying too much about facts and figures and pressure etc though I am intrigued to know how you managed to get pressure figures to one decimal point, standard pressure gauges aren't that accurate.

If the system is filthy and you can get a magnet to stick to certain spots then that is a certain indication that there are restrictions to flow and the pump can't circulate properly and the boiler is exceeding it's high set limit, hence the cycling.

If it's go to the point where you can attach a magnet to sections then cleaner will not be able to shift that amount of build up, it may get better but you'd be there for ever and a day to clear it all out. Time to start checking and replacing fittings/pipe section, strip the pump out as that may have become clogged up after the clean, that and the boiler's HEX/internals may also be restricted now but that's a whole different ball game.

I assure you I'm not worrying about facts and figures, but I do wonder about the quality of advice of someone who holds them in such disdain. Here is how how I managed to measure pressures to 1 decimal place.

 

[mjburrows]

Moved into 4 bed detached Victorian house last year. Wasn't particularly warm over winter and have decided to investigate. Found boiler is short cycling, 2 minutes on 2 minutes off. Boiler switches off when outlet temp reaches about 75 C, and inlet temp is 55 C. Cleaned out system with Sentinel x800, but that has had no effect.

Found bypass valve was always open so took that off and found it jammed with black gunge. Put in a new one which stayed closed until I foolishly turned down pressure, now that one will not close!. Replaced it temporarily with stop ends.

Knowing boiler output and delta temp over output, calculated flow rate through primary and hot water tank circuit at 16 litres / min. Have put pressure gauge where bypass was, after pump and before motorised valves. Static pressure is 1.7m. This increases to 2.4m (0.7m above static) when pump is running and hot water tank circuit motorised valve is open. Gauge reads 3.2m (1.5m above static) when pump is running and valves are closed. Pump is BG Grundfos multihead G that I cant find curves for. Pump setting 3. Have curves for selectric and super selectric which I understand are similar and give a maximum head of 5 to 6 metres, and a head of 4.5 to 5 metres at a flowrate of 16 litres / min

So it looks as if the pump isn't producing the required flowrate and head. The piping immediately before and after the pump strongly attracts a magnet, and water drained from the pump is dirty. Could the dirt be affecting the pump? If I replace the piping could I clean the pump? I see there are cheap refurbished BG Grundfos multihead Gs available - are they any good? I'd love to hear your thoughts on how to proceed. Thanks

All fixed now! Thanks to everyone who helped.

Here is how I would proceed if faced with short cycling again.
1. Check room thermostat working properly
2. Buy a digital thermometer with two sensors like this https://www.amazon.co.uk/dp/B071RNW2C6?psc=1&ref=ppx_yo2ov_dt_b_product_details and some clips like these https://www.amazon.co.uk/dp/B07BL3MY7G?psc=1&ref=ppx_yo2ov_dt_b_product_details. Use these to monitor the output temperature of the boiler to establish if the boiler thermostat is working as expected.
3. Check the difference between boiler input and output temperature. If this over 20C as mine was this is suggestive of poor circulation.
4. If the pump is making a lot of noise there is a good chance the impellor is full of crap. It's not a huge job to remove the pump and clean out the impellor and that may be all you have to do.
5. The piping near the feed to the central heating circuit on my system attracted a magnet so I cut it out. But there was no need as the amount of crap was quite small. This was a difficult bit of work that didn't turn out to be necessary.
6. My header tank was full of crap, so I drained that and removed the crap.

 

[fixitflav]

"strip out the pump" isn't that helpful unless you say what to do with it once it's stripped out. And all the evidence I have suggests the impeller was jammed with crap before the clean.

But as you said in #15, you cleaned out the crap, and got a big improvement. So I assume what needed doing was obvious once you'd dismantled it.

 

[Madrab]

"strip out the pump" isn't that helpful unless you say what to do with it once it's stripped out. And all the evidence I have suggests the impeller was jammed with crap before the clean.

Of course it is, 2 people suggested to look at the pump, how it is described is inconsequential. The first thing to be done would be to strip down the pump to get to the impeller, then it would be seen that it's filled with crap from the system and that would cause the poor circulation. Whether it was clogged before or after is inconsequential, it needed stripped down and the internals cleaned out. Can't really be much clearer or more helpful IMO.

I assure you I'm not worrying about facts and figures, but I do wonder about the quality of advice of someone who holds them in such disdain. Here is how how I managed to measure pressures to 1 decimal place.

As suggested, standard gauges wouldn't go to that level of accuracy and it would be strange to see someone on here asking for DIY advice with that sensitive level of equipment. CH engineers wouldn't even have that as part of their usual toolkit. I don't hold any of the figures is disdain, neither did I suggest I did. All I said it that level of detail doesn't need to be focused on when it comes to fault finding poor circulation on a CH system, especially give the original info. This is a DIY site and it would be very unusual for anyone to go to that level for fault finding and fixing a circulation issue.

I'm sorry that you don't like the way things are suggested but time is precious and most are here to get straightforward and to the point advice to help fix the issue quickly.

 

[Bod ...]

Needs a Power Flush I believe. A chemical flushes merely agrivates debris so thst it now travels the system.

A Big Pand a big F will set you on the right road. Attach in place of tye pump. Then clean pump while flushing.

 

[mjburrows]

Of course it is, 2 people suggested to look at the pump, how it is described is inconsequential. The first thing to be done would be to strip down the pump to get to the impeller, then it would be seen that it's filled with crap from the system and that would cause the poor circulation. Whether it was clogged before or after is inconsequential, it needed stripped down and the internals cleaned out. Can't really be much clearer or more helpful IMO.

As suggested, standard gauges wouldn't go to that level of accuracy and it would be strange to see someone on here asking for DIY advice with that sensitive level of equipment. CH engineers wouldn't even have that as part of their usual toolkit. I don't hold any of the figures is disdain, neither did I suggest I did. All I said it that level of detail doesn't need to be focused on when it comes to fault finding poor circulation on a CH system, especially give the original info. This is a DIY site and it would be very unusual for anyone to go to that level for fault finding and fixing a circulation issue.

I'm sorry that you don't like the way things are suggested but time is precious and most are here to get straightforward and to the point advice to help fix the issue quickly.

I don't really expect someone who suggests I shouldn't worry about facts to concern himself about the difference between "strip out", meaning "remove", and "strip down" meaning "disassemble". If it's inconsequential whether or not the crap got into the pump before after the clean, why mention it?. I'm not disputing that you mentioned "standard" gauges, whatever they are, simply answering your query.

 

[SpecialK]

Good suggestion. The impeller was nearly full of baked in crap. I spent 20 mins poking it out with a bit of stiff wire and now produces a 5m head rather than the 1.5m before. Thanks!

Time for a mechanical and magnetic filter to be installed?

 

[Madrab]

Jeesh, all I said was that level of detail wasn't required, if you didn't understand that from my comment and took it as a slight on your professional acumen or as a person criticism, then can I suggest you familiarise yourself with forums like this and grow a thicker skin.

If you wish to play with semantics over what 'strip out' means when it comes to a pump and it's housing then knock yourself out. It seems that others more familiar with CH systems, quite clearly understand what that means and if you didn't and just wish to make a point over nothing then I'll leave you to it.

I'll go back to giving my time and advice to others here that appreciate it.

 

[mjburrows]

Time for a mechanical and magnetic filter to be installed?

Yes. My fix was really only intended to get us through the winter. Will probably be replumbing and putting in a new boiler next year once some other jobs are done.

 

[mjburrows]

Jeesh, all I said was that level of detail wasn't required, if you didn't understand that from my comment and took it as a slight on your professional acumen or as a person criticism, then can I suggest you familiarise yourself with forums like this and grow a thicker skin.

If you wish to play with semantics over what 'strip out' means when it comes to a pump and it's housing then knock yourself out. It seems that others more familiar with CH systems, quite clearly understand what that means and if you didn't and just wish to make a point over nothing then I'll leave you to it.

I'll go back to giving my time and advice to others here that appreciate it.

I have no professional acumen in central heating and i'm not in the slightest bit emotionally affected by anything you've written. I think it is you who needs to grow a thicker skin. Your whining over who provided me with the crucial piece advice of suggests to me that is you that emotionally over invested in this forum.

What words mean matter. I simply don't believe that CH experts have a different understanding of "strip out" and "strip down" from everyone else. And even if they did, wouldn't they make that clear to rank amateurs like me?