Whole House Hot Water Pump hesitating

[LittleJoe]

For just over a year I have had a Techflow Turbo 2 Twin Negative head pump in the loft servicing the whole house hot water including the bathroom and en-suite showers. The installation was surveyed and approved by Techflow at that time. The system has been working fine.
Recently I have noticed that when a hot tap is on and the pump is delivering hot water the pump momentarily switches off or hesitates occassionally. I have tried adjusting the hot flow switch fractionally but this results in the pump staying on when the taps are turned off so I have adjusted the switch back and still get the problem.
Has anyone any thoughts on what might be causing this?

 

[Axel]

Is there an expansion vessel on / near the pump? Maybe this needs re-charging. It could be that when you turn on the hot tap, the pressure drop activates the pump which creates a pressure pulse that momentarily turns the pressure switch off while hot is running. A functional expansion vessel on the output pipework of the pump wil buffer this pulse. If it was originally ok but has now started doing this, it is either an issue with any built in expansion vessel, absence of one, or the sensitivity of the pressure switch has changed. Negative head pumps use a pressure switch unlike positive head pumps that activate on detecting flow.

 

[LittleJoe]

There is an expansion vessel on top of the pump (this is a small cylinder about 10cm diameter, about 10cm high with what looks like a schraeder tyre valve on the top !!) How do you recharge this vessel?
As mentioned I have tried adjusting the flow switch without curing the problem. The Techflow pump is still under warranty, so if there is a problem with the pressure switch I can always get a replacement.

 

[Axel]

To check the air charge on the little expansion vessel you need to:

0. Switch off electrical power for pump
1. Turn off inlet pipes to pump
2. Open outlet pipes to depressurise pump (taps!)
3. Put a tyre pressure gauge ( a good old manual 'pen' type - not some fancy electronic thing from argos) onto the Schrader valve on top of the expansion vessel.
4. I don't know what pressure it should be - maybe in the manual or online or even on the vessel itself - maybe a bar, bar and a half.
5. If the pressure is too low then recharge it with a bicycle pump.
6. Open valves, turn on power and see if there is any improvement.

 

[LittleJoe]

Axel,
Thanks for this. I will give this a try tommorrow and post the results.

Regards

 

[LittleJoe]

Axel,
I didn't get chance to carry out the recharging of the expansion vessel today as you suggest, but I did talk to Techflow pumps ' technical Helpline.
Their suggestion was to first investigate whether the hot water temperature is too hot flowing through the pump as this can cause cavitation around the impeller which can result in the pump thinking there is a momentary interruption of flow, which would momentarily switch the pump off and on.
I have felt the hot water was a little hot recently so I did lower the cylinder stat. temperature (and the boiler temp slightlyalso) and then after a while I ran the hot taps. The problem still existed even when the hot water was running virtually cold, although the momentary interruptions weren't as bad and seemed to mainly happen with a mixer tap on the en-suite hand basin.
I raised your suggestion of the expansion vessel with Techflow. They didn't rule this out but felt it was unlikely. Their explanation being that the vessel is only helping to get the flow started and once flow is started, it normally continues until flow is stopped at the tap. Once flow is started the vessel doesn't have any influence.
They wanted me to check the hot water temperature first and if that doesn't eliminate the problem, they said that the vessel may be worth investigating. I will speak to them tomorrow and give them the feedback on the water temp test. I avoided the recharge of the vessel today mainly because I wasn't sure what pressure should be used. I found the Zilmet Expansion vessel website and from waht I could gleen, the 'precharge' pressure is 3.5 Bar (50 PSI) which seems quite high. This made me a bit nervous about getting my car footpump out !!!!
I'll keep you updated.
Regards

 

[LittleJoe]

OK. I spoke with Techflow (who are now owned by Stuart Turner Pumps !!) and advised that reducing the hot water temperature has not eliminated the flow hesitation problem.
I raised the recharging of the expansion vessel and agreed that I should try that next. They said I should charge the vessel to 0.9 Bar (13 psi).
I have now carried out a recharge on the expansion vessel and the problem still exists. I have tried the expansion vessel at 0.8 bar, 0.9 bar and 1.6 bar but at each pressure the pump still hesitates every now and then.
The problem seems to manifest itself mainly on a monobloc mixer tap in my en-suite sink. The Stuart Turner engineer suggested that the thin tails that connect this monobloc mixer tap could cause such a problem. Having said this, the whole system has worked perfectly for over a year. This problem has only started in the past month.
I am still no further on in sorting this problem. I will talk to the Stuart Turner engineers again tomorrow and see what else they can suggest. They may end up sending out an engineer as the pump is still under warranty.
Anyway, thanks for your help so far Axel.

Regards

 

[xr4x4]

i like their diagnostics...it could be anything...!!

 

[LittleJoe]

Well I can't fix it, so I am open to any suggestions !!!

 

[LittleJoe]

Update: Techflow are sending out an Engineer to investigate the problem.

 

[Axel]

Please update us when he is done!

Thanks.

 

[LittleJoe]

Axel,

Will do.

Regards

 

[LittleJoe]

Latest Update:

A Techflow Engineer is booked for 27th January 2011 and he is bringing a replacement pump (Twin Turbo 2 , Negative Head).

Regards

 

[Axel]

I guess we'll never know...!!

 

[LittleJoe]

Axel,

Yes we will !!!

Well the Techflow Service Engineer visited. He couldn't fault the installation and plumbing. He concluded that it must be the pump and fitted a brand new Twin Turbo 3 Negative Head pump to replace the existing Turbo 2. Result.... the same problem existed but now the pump kept running on and every 10 seconds or so would hesitate ie. momentarily shut off then on again.
Despite adjusting the reed switches, and in fact removing them completely, the pump ran on !!! If both the pump outlet isolating valves were closed, the pump ran on when all outlets (taps) were closed. Occasionally. if you opened and closed a tap, the pump would shut off. We also continued to get the hesitation.
The Techflow engineer made some other checks on the pump and he concluded there was something wrong with the PC Control Board in the pump. (This was a new pump !!??) Seemed a hell of a coincidence.
Anyway, as Techflow are now owned by Stuart Turner Pumps, the Techflow engineer called Head Office and arranged for a new Stuart Turner Monsoon Universal Twin 3.0 Bar pump to be despatched to replace the Techflow pump.

I removed the Techflow pump on 8 Feb and fitted the Monsoon and the system is working absolutely fine !!!!

I have made no changes to the plumbing except for minor pipework changes to marry up with the Monsoon inlets and outlets. I took the opportunity to mount the pump on a piece of concrete paving slab. The pump is much quieter than the Techflow. (The concrete slab has made quite a bit of difference.)

Conclusion: The original Techflow pump worked for a year before exhibiting problems. The replacement Techflow pump - just bad luck !!

I certainly would only use a Stuart Turner pump in future. Since Techflow are now owned by Stuart Turner maybe the product range will be rationalised, and all the best design features of the Stuart Turner pumps will be integrated into any new pump designs.

Hope that closes the whole saga now !!!