Atag boiler short cycling

[D_Hailsham]

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I can't work out which way is up on this pic. It looks as if the pump is lying on the floor pointing upwards which, if it is, is the worst way to install a pump as it will wear out very quickly due to lack of lubrication. The pump shaft mut always be horizontal.

If the pump is installed as at appears in the pic, it could already be worn out as the flow/return differential (A2-A1) of nearly 30 degrees says that the flow rate is much too low, which could indicate a damaged pump.

You asked about A1 and A2 being the same when the boiler cuts out. Do you mean when the flame goes off or when the pump stops working? Normally there will be a noticeable temperature differential until the flame goes out, but this will reduce as the pump continues to run for a few minutes (pump overrun).

 

[Jon c]

View attachment 222822
I can't work out which way is up on this pic. It looks as if the pump is lying on the floor pointing upwards which, if it is, is the worst way to install a pump as it will wear out very quickly due to lack of lubrication. The pump shaft mut always be horizontal.

If the pump is installed as at appears in the pic, it could already be worn out as the flow/return differential (A2-A1) of nearly 30 degrees says that the flow rate is much too low, which could indicate a damaged pump.

You asked about A1 and A2 being the same when the boiler cuts out. Do you mean when the flame goes off or when the pump stops working? Normally there will be a noticeable temperature differential until the flame goes out, but this will reduce as the pump continues to run for a few minutes (pump overrun).

Yes the silver screw cap on the pump is pointing upwards, I'll turn it horizontal but it's been this way for 12 years probably. Is there any way to test whether it is working correctly as a new one is rather expensive and I'd rather not go replacing random parts if it's unnecessary? With regards to the flow and return difference, it's always 20-30 degrees difference at the point the flame goes out, and yes the pump does keep running. Also both values do get similar a few minutes afterwards, say if the boiler cut out at 80 ish after a few minutes both flow and return will be around 50-60. Obviously lower if the boiler cuts out at a lower temp. Perhaps explains why the boiler temp was set so high - the installers knew there was a problem with low circulation?

 

[vulcancontinental]

If it was a new build developers are not inclined to oversize radiators so if they were sized for certified output they need a 75degree C flow into them in these weather conditions only if they're over sized could you consider reducing the flow temp. Search Heat Engineer and do a heat loss on the house, a thorough one off will cost you a tenner and a few hours, the free one would not be as accurate. Range rate the boiler once you've done that. I don't know whether that's possible with an Atag but would expect to be so.

 

[Jon c]

If it was a new build developers are not inclined to oversize radiators so if they were sized for certified output they need a 75degree C flow into them in these weather conditions only if they're over sized could you consider reducing the flow temp. Search Heat Engineer and do a heat loss on the house, a thorough one off will cost you a tenner and a few hours, the free one would not be as accurate. Range rate the boiler once you've done that. I don't know whether that's possible with an Atag but would expect to be so.

Yes it was a new build, they seem reasonably sized based on the room size and insulation and amount of windows, but would only be effective if they actually got up to temp. The kitchen one for instance is a double panel 600x1400mm as the room (approx 5x5m) has a number of floor to ceiling windows, but it never gets very warm due to the excessively long microbore pipe run to it although I think it would be more than capable of heating the room if it got up to temp.
I don't think any of them have a consistent 75⁰c flow, couple of the upstairs ones might get near at times but no way any of the downstairs ones get anywhere near this - they are never even slightly uncomfortable to touch. I don't have a thermal imaging camera unfortunately so can't take rad temp readings, I'm just going off my judgement bearing in mind when the boiler flow temp reads around 75 there's no way I can comfortably touch the pipe. Will look into the heat engineer thing.

 

[MJN]

I don't have a thermal imaging camera unfortunately so can't take rad temp readings

An IR thermometer or pipe clamps will tell you the flow and return readings - the average of those will equal the average temperature across the radiator.

 

[MeldrewsMate]

Would you expect the return temp to be similar to the flow temp at the point the boiler turns off?

Not necessarily. The boiler will normally turn off when the system water temperature continues to rise even though it has modulated to its lowest output. In the case I've just described the two temperatures, flow and return, will be close together.
In your case I suspect low flow through the boiler therefore, even at low output, the temperature gradient across the boiler will be high when the desired flow temperature has been reached.

(Now I'm going to read the rest of this thread back to my last post in the hope that you've added some evidence.)

 

[MeldrewsMate]

...I will try dismantling the pump tomorrow...

Jon C, it's tomorrow already. What is the outcome of inspecting and cleaning the circulating pump?

 

[Jon c]

Jon C, it's tomorrow already. What is the outcome of inspecting and cleaning the circulating pump?

Sorry I forgot to post about that, it didn't look too badly gunged up inside and I tried to give it a clean, hasn't seemed to have any effect though. I should have taken some photos, sorry I didn't think to at the time. I have also now orientated it horizontally, which also has not changed anything, I suppose if its damaged from being mounted incorrectly for so long it's not really reversible. Would it be worth changing the pump out as it's 12 years old anyway to see it it makes any difference?

 

[Jon c]

Just another though, could the pump be undersized? It's a grundfos UPS 15-60 130. Bearing in mind there are 13 rads and a megaflo do you think it's probably correctly sized?

 

[MeldrewsMate]

...Would it be worth changing the pump out as it's 12 years old anyway to see it it makes any difference?

Clearly it's your money. but that would be my recommendation given the evidence presented. Get one that can achieve 6m of head, as that will beter serve your microbore rads.

Are you sure the pump was clear? Nothing came out when you rodded all 12 (?) impellor ports? Was the base clear of deposits too? Not sure what 'not too badly gunged-up' might mean.

 

[Jon c]

Clearly it's your money. but that would be my recommendation given the evidence presented. Get one that can achieve 6m of head, as that will beter serve your microbore rads.

Are you sure the pump was clear? Nothing came out when you rodded all 12 (?) impellor ports? Was the base clear of deposits too? Not sure what 'not too badly gunged-up' might mean.

There was nothing large at least, just little black bits as would probably be expected. Nothing large came out of the ports. Base was clear although a little rusty. It was able to spin fairly freely, and no obvious damage to any parts, but as has been said who knows if it is actually working at the right speed. There isn't anything I can do to test it really is there? Also what do you mean by '6m of head' ? Is that the length of the legs to the rads?

 

[Jon c]

There was nothing large at least, just little black bits as would probably be expected. Nothing large came out of the ports. Base was clear although a little rusty. It was able to spin fairly freely, and no obvious damage to any parts, but as has been said who knows if it is actually working at the right speed. There isn't anything I can do to test it really is there? Also what do you mean by '6m of head' ? Is that the length of the legs to the rads?

Actually I should mention when I set it to the 2nd or 1st speed settings the motor sometimes makes a buzzing sound as if it is trying to start up but can't, this only happens if it has stopped completely before trying to start, and I will get going eventually. Fastest speed setting does not do this, it runs normally and starts without a problem. Now it was doing this before and after I took it apart so even though it could spin freely when in pieces maybe it is getting a bit stuck when its put together? No obvious reason I could see though.

 

[MeldrewsMate]

Mentioned before by others, 'lazy pump'. I would even more suggest changing the pump now.

 

[Jon c]

Mentioned before by others, 'lazy pump'. I would even more suggest changing the pump now.

Fair enough I will do that, should I go for an exactly equivalent replacement? Also if that doesn't help whats the next thing to look at?

 

[MeldrewsMate]

Read back, I told you what type of pump to get. The old Grundfos are no longer available (50 made redundant, so clearly I won't recommend that make)