CH Circulation pump (?) fault diagnosis

[Spectric]

Many think of Grunfoss as the pump rather like Hoover has become the name for a vacuum cleaner, they are a fit and forget item provided the system is clean and maintained but it is amazing how many still get fitted into the boiler output and not the return where they can have a cooler life. I suspect it is a carry over from the days when we had header tanks and not sealed systems.

 

[1steven]

Many think of Grunfoss as the pump rather like Hoover has become the name for a vacuum cleaner, they are a fit and forget item provided the system is clean and maintained but it is amazing how many still get fitted into the boiler output and not the return where they can have a cooler life. I suspect it is a carry over from the days when we had header tanks and not sealed systems.

Most are fitted to the flow now from the pump into the zone valves etc. Industry standard for energy efficiency.

 

[Spectric]

Most are fitted to the flow now from the pump into the zone valves etc. Industry standard for energy efficiency.

Not on the last courses I did, ok a while back but the logic is sound. With a sealed system at pressure then a pump circulating into the boiler is still effectively moving water to the zone valves except it is not moving heated water but cooler return flow to be heated. There is no longer the risk of drawing air into the system like when we had header tanks and expansion pipework, the bigger issue is with the bypass and smart pumps.

 

[Just4Fun]

I have skip read this ....

I don't blame you. The system is relatively complicated and there is a lot of information here, mostly red herrings.

The 2 pumps mentioned to date are on the radiator circuit. There is another pump on the field loop that I have not mentioned so far. The problem is, I believe, on the radiator circuit so I have not wanted complicate things even more by going down the field loop rabbit hole.

 

[Just4Fun]

130859 <- link is quite a useful guide, you probably know all that's in there already but might be worth a look

Indeed. Some excellent information there.

 

[Just4Fun]

Had a couple of Grundfos let go but, as you say, the Wilos are known for it.

Does this problem ever happen in such a way that the pump works sometimes and not at others? I haven't yet got any theory to explain why the problem is intermittent.

 

[Spectric]

A simple sketch would have made everything much clearer, they do say a picture is worth a thousand words !

 

[Bingy man]

Most members have responded to this thread with a normal domestic system in mind ( as I did ) but if you re read the op he mentions ( a million rads) obviously a slight exaggeration but that’s why I asked how many rads , a system of this size has probably had a multitude of plumbers and heating engineers working on it over its life and they have all probably done what they thought was the best fix to cure the problems as they have arisen. Sometimes although the cost would be horrendous it’s a case of “ back to the drawing board “ to re design the system to make it more efficient and easier for future engineers to understand. Something I mentioned earlier is the quality of the water in the heating circuit, the age and type of the rads fitted, the likelihood of sludge deposits given it’s mainly iron pipe work ( and lots of it ) very likely that at some point a commercial heating engineer will be required to assess and make the necessary modifications to improve the system efficiency. Op says some of the rads are turned off so what happens should they all be turned on? I don’t know a lot about gshp but recognise that similar to condensing boiling if the system is not up to scratch and fit for purpose then any efficiency savings are lost along the way. I’m currently gutting a 6 bedroom house that originally had an oil system / floor standing cast iron rads and large bore iron pipe work with a floor standing boiler the size of a 6 x 8 shed . Too big a job for me alone in terms of size of the property and the time constraints but an x b,gas engineer and friend of mine are likely to go with an unvented hot water system ( solar compatible) and at least 2 possibly 3 heating zones . No easy task as the property has been empty for years.

 

[Skydivermel]

You need to interlock the 2 pumps on the radiator circuit. Simple to do

 

[pe2dave]

Series vs parallel water pumps had me.
this article provides an answer.

 

[Spectric]

I would have thought in that article they must be positive displacement pumps for that to hold true. With circulators they do not move a fixed volume per revolution and If dead headed will just keep turning wheras a positive dispalcement pump does move a certain volume per revolution and if dead headed will generate pressure until something gives.