Hot water cylinder only warms up when CH pump off

[burt32]

Dear all, open to any suggestions to overcome this problem.
Scenario is hot water cylinder (gravity fed) only warms up when heating pump goes off.
Boiler has 4 pipes (2 at top 22mm flow CH and 28mm flow DHW) and 2 returns at bottom. Had a problem with circulation this winter so changed pump to Grunfos 15-60. Circulation issues cured (pump running on speed 1) but now when boiler comes on the DHW flow is working in reverse as if the pumped return is pumping back up what should be the return from HW cylinder. When heating satisfied eventually the hot water cylinder starts to warm with heating returning to what should be the flow to the cylinder (top pipe).
Could I fit a check valve on the return from cylinder?
Hope I have explained this enough for some advice.

 

[Best]

What sort of boiler is it?
If it is oil or gas, it will be faster to heat up if converted to all pumped - which is how all modern jobs must be done. Needs an engineer to do this, but.
If solid fuel, then gravity is normal to hot tank.
Either way, you can have what is called an injector tee fitted on the returns at the boiler & that maintains circulation to cylinder & the correct direction, while pump is on to heat rads.

 

[burt32]

Hi Best,

Thanks for speedy reply, boiler is gas fired Halstead Best 60.

I understand it would be best to convert to S or Y plan but problem only occurred since fitting new pump. Previous pump was about 5 years old and reused when boiler was fitted in 2002ish.

Really only noticed lack of hot water since introduction of second bathroom and more use of hot water at once.

So the injector Tee may sort out the problem rather than a simple check valve on DHW return.

 

[Best]

Check valve is a no no on gravity pipes. And if it is the spring type check valve, then it will stay shut.
Be careful your new pump is fitted correct direction of flow.
Gravity circuit will be affected by the pump if no injector tee.
Some of the gas guys might advise you.

 

[REDSAW]

pumps on wrong way round!

 

[burt32]

Double checked, pump is on the correct way round, ie on flow from boiler.

 

[Mike Jackson]

It is not possible to use an injector tee with this boiler so the problem is possibly caused by having the pump on the return. The instructions only show the pump on the flow which will create a zone of lower pressure at the bottom of the boiler. Having the pump on the return could created a higher pressure zone at the bottom effectively blocking the gravity circulation. This problem will be exacerbated with a more powerful pump.

 

[burt32]

Mike,

The pump is on the flow as shown in the installation configuration for this boiler. You state that it is not possible to fit an injector "T" on this type of boiler so this issue appears to be a puzzle with the only answer to convert to S or Y plan.